Apparatus and buffer control method thereof in wireless communication system

ABSTRACT

A 5G communication system or pre-5G communication system for supporting a higher data rate than that of a beyond 4G communication system such as an LTE is provided. A method by an apparatus for controlling buffers in a wireless communication system comprises storing information related to a packet in at least one of a first buffer or a second buffer, transmitting data generated based on the packet, and, when an acknowledgement signal is received for the data, discarding the information.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 15/942,972, filed on Apr. 2, 2018, which was based on and claimedpriority under 35 U.S.C § 119(a) of a Korean patent application number10-2017-0041702, filed on Mar. 31, 2017, in the Korean IntellectualProperty Office, and a Korean patent application number 10-2017-0058498,filed on May 11, 2017, in the Korean Intellectual Property Office, thedisclosure of each of which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The disclosure relates to operations of a terminal and a base station ina next-generation mobile communication system. More particularly, thedisclosure relates to a method for a terminal and a base station toefficiently manage a buffer, and a method and an apparatus capable ofaccelerating retransmission during the retransmission.

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, hybrid FSK and QAM modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed. On the other hand, in thenext-generation mobile communication system, there is a need for amethod for a base station to efficiently manage a buffer and a methodcapable of accelerating retransmission.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providea method for efficiently managing a buffer and implementation methodsthereof in different buffer structures. Further, the disclosure proposesmethods for accelerating retransmission and efficiently managing abuffer in a next-generation mobile communication system, andimplementation methods thereof in different buffer structures.

In accordance with an aspect of the disclosure, a method by an apparatusfor controlling buffers in a wireless communication system is provided.The method includes storing information related to a packet in at leastone of a first buffer or a second buffer, transmitting data generatedbased on the packet, and, when an acknowledgement signal is received forthe data, discarding the information.

In accordance with another aspect of the disclosure, a method by anapparatus for controlling buffers in a wireless communication system isprovided. The method includes storing first information related to afirst packet in a third buffer; storing second information related to asecond packet in a fourth buffer, wherein the second information isgenerated by preprocessing the first packet before acquiring resourceinformation for transmitting the first packet; identifying mappinginformation between location information of the third buffer andlocation information of the fourth buffer, and when the resourceinformation is received, transmitting data corresponding to the secondpacket based on the resource information.

In accordance with another aspect of the disclosure, an apparatus in awireless communication system is provided. The apparatus includes atransceiver and at least one processor configured to store informationrelated to a packet in the at least one of the first buffer or thesecond buffer, transmit data generated based on the packet, and, when anacknowledgement signal is received for the data, discard theinformation.

In accordance with another aspect of the disclosure, an apparatus in awireless communication system is provided. The apparatus includes atransceiver and at least one processor configured to store firstinformation related to a first packet in a third buffer, store secondinformation in a fourth buffer, the second information being related toa second packet that is generated by preprocessing the first packetbefore acquiring resource information for transmitting the first packet,identify a mapping information between location information of the thirdbuffer and location information of the fourth buffer, and, when theresource information is received, transmit data corresponding to thesecond packet based on the resource information.

According to the embodiments of the disclosure, it is possible toheighten efficiency of the buffer management of the terminal and toincrease the data rate.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram illustrating the structure of a long term evolution(LTE) system according to an embodiment of the disclosure;

FIG. 2 is a diagram illustrating a radio protocol structure of an LTEsystem according to an embodiment of the disclosure;

FIG. 3 is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of thedisclosure;

FIG. 4 is a diagram illustrating a radio protocol structure of anext-generation mobile communication system according to an embodimentof the disclosure;

FIGS. 5A and 5B are diagrams illustrating a data processing structure inan LTE system according to an embodiment of the disclosure;

FIG. 6 is a diagram illustrating a first embodiment of an efficientbuffer management method suitable when an LTE system terminal operatesin a radio link control (RLC) acknowledged mode (AM) according to anembodiment of the disclosure;

FIG. 7 is a diagram illustrating a mapping table and a correspondingoperation of an efficient buffer management method when an LTE systemterminal operates in an RLC AM mode according to an embodiment of thedisclosure;

FIGS. 8A and 8B are diagrams illustrating the operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode inaccording to an embodiment of the disclosure;

FIGS. 9A and 9B are diagrams illustrating the operation of a terminal inwhich an LTE system terminal manages buffers in an RLC unacknowledgedmode (UM) in according to an embodiment of the disclosure;

FIGS. 10A and 10B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode inaccording to an embodiment of the disclosure;

FIGS. 11A and 11B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC UM mode inaccording to an embodiment of the disclosure;

FIG. 12 is a diagram illustrating a mapping table and of a buffermanagement method suitable when an LTE system terminal operates in anRLC AM mode according to an embodiment of the disclosure;

FIGS. 13A and 13B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode accordingto an embodiment of the disclosure;

FIGS. 14A and 14B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC UM mode accordingto an embodiment of the disclosure;

FIGS. 15A and 15B are diagrams illustrating a data processing structurein a next-generation mobile communication system according to anembodiment of the disclosure;

FIG. 16 is a diagram illustrating a mapping table and a retransmissionacceleration method suitable when a next-generation mobile communicationsystem terminal operates in an RLC AM mode proposed according to anembodiment of the disclosure;

FIGS. 17A and 17B are diagrams illustrating operation of a terminal inwhich a next-generation mobile communication system terminal managesbuffers in an RLC AM mode according to an embodiment of the disclosure;

FIGS. 18A and 18B are diagrams illustrating operation of a terminal inwhich a next-generation mobile communication system terminal managesbuffers in an RLC UM mode according to an embodiment of the disclosure;

FIG. 19 is a block diagram of a terminal according to an embodiment ofthe disclosure;

FIG. 20 is a block diagram of a transmission and reception point (TRP)in a wireless communication system according to an embodiment of thedisclosure; and

FIG. 21 is a diagram illustrating a method for preprocessing data of amulti-connection terminal according to an embodiment of the disclosure.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In describing the disclosure, related well-known functions orconfigurations incorporated herein are not described in detail in thecase where it is determined that they obscure the subject matter of thedisclosure in unnecessary detail. Hereinafter, embodiments of thedisclosure will be described with reference to the accompanyingdrawings.

Hereinafter, terms for identifying a connection node, terms for callingnetwork entities, terms for calling messages, terms for calling aninterface between network entities, and terms for calling various piecesof identification information, as used in the following description, areexemplified for convenience in explanation. Accordingly, the disclosureis not limited to the terms to be described later, but other terms forcalling subjects having equal technical meanings may be used.

Hereinafter, for convenience in explanation, terms and titles that aredefined in the 3^(rd) generation partnership project long term evolution(LTE) standards are used in the disclosure. However, the disclosure isnot limited by the terms and titles, but can be equally applied tosystems following other standards.

In a next-generation mobile communication system, it is necessary tosupport a peak data rate of 20 Gbps in a downlink and a peak data rateof 10 Gbps in an uplink, and quite a short delay response time isrequired. Accordingly, in case of a terminal being serviced in thenext-generation mobile communication system, quite a hightransmission/reception data processing speed is necessary. Accordingly,a method for accelerating data processing of a terminal is important.Further, in order to support the high data rate and to accelerate thedata processing speed, efficient buffer management is also important. Ina mobile communication system, one of the biggest causes of greatlylowering the data rate is a latency due to retransmission. Accordingly,in order to support the high data rate in the next-generation mobilecommunication system, it is necessary to accelerate the retransmission.

An LTE system has a data processing structure different from that of thenext-generation mobile communication system. Specifically, in the LTEsystem, an radio link control (RLC) layer perform an RLC concatenationfunction, and thus a terminal is unable to perform a certain datapreprocessing until it receives an uplink transmission resource from anetwork. If the uplink transmission source is received, the terminalmakes and transmits one RLC packet data unit (PDU) to a media accesscontrol (MAC) layer through concatenation of packet data convergenceprotocol (PDCP PDUs transmitted from a PDCP layer to proceed with datatransmission.

In contrast, in the next-generation mobile communication system, an RLClayer does not have an RLC concatenation function, and thus a terminalhas a data processing structure capable of making and transmitting anRLC PDU to a MAC layer by processing PDCP PDUs transmitted from a PDCPlayer through the RLC layer before receiving an uplink transmissionresource, and pre-generating a MAC sub-header and MAC service data unit(SDUs).

Accordingly, it is necessary to implement a method for efficientlymanaging buffers and a method for accelerating retransmission indifferent methods in accordance with different data processingstructures.

FIG. 1 is a diagram illustrating the structure of an LTE systemaccording to an embodiment of the disclosure.

Referring to FIG. 1, as illustrated, a radio access network (RAN) of anLTE system is composed of evolved node ENBs) 105, 110, 115, and 120(also referred to as base stations), a mobility management entity (MME)125, and a serving-gateway (S-GW) 130. A terminal or a user equipment(UE) 35 accesses an external network through the ENBs 105 to 120 and theS-GW 130.

In FIG. 1, the ENB 105 to 120 corresponds to an existing node B of aUMTS. The ENB is connected to the UE 135 on a radio channel, and plays amore complicated role than that of the existing node B. In the LTEsystem, since all user traffic includes a real-time service, such as avoice over (VoIP) through an internet protocol (IP) are serviced onshared channels, devices performing scheduling through consolidation ofstate information, such as a buffer state, an available transmissionpower state, and a channel state of each UE, are necessary, and the ENBs105 to 120 correspond to such scheduling devices. In general, one ENBcontrols a plurality of cells. For example, in order to implement atransmission speed of 100 Mbps, the LTE system uses, for example,orthogonal frequency division multiplexing (OFDM) in a bandwidth of 20MHz as a radio access technology. Further, the LTE system adopts anadaptive modulation & coding (AMC) scheme that determines a modulationscheme and a channel coding rate to match the channel state of theterminal. The S-GW 130 provides a data bearer, and generates or removesthe data bearer under the control of the MME 125. The MME controlsmobility management of the terminal and various control functions, andis connected to the plural base stations.

FIG. 2 is a diagram illustrating a radio protocol structure of an LTEsystem according to an embodiment of the disclosure.

Referring to FIG. 2, in an UE or an ENB, a radio protocol of an LTEsystem is composed of a PDCP 205 or 240, a RLC 210 or 235, and a MAC 215or 230. The PDCP 205 or 240 takes charge of IP headercompression/decompression operations. The main functions of the PDCP aresummarized as follows.

-   -   Header compression and decompression: robust header compression        (ROHC) only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs at a PDCP        reestablishment procedure for a radio resource control (RRC)        acknowledged mode (AM)    -   For split bearers in dual connectivity (DC) (only support for an        RLC AM): PDCP PDU routing for transmission and PDCP PDU        reordering for reception    -   Duplicate detection of lower layer SDUs at a PDCP        reestablishment procedure for an RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at a PDCP data-recovery procedure, for an        RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in an uplink

The RLC 210 or 235 reconfigures a PDCP PDU with a proper size andperforms an automatic repeat request (ARQ) operation and the like. Themain functions of the RLC are summarized as follows.

-   -   Transfer of upper layer PDUs    -   Error correction through an ARQ (only for AM data transfer)    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for UM and AM data        transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer)    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM transfer)    -   RLC reestablishment

The MAC 215 or 230 is connected to several RLC layer devices configuredin one terminal, and performs multiplexing/demultiplexing of RLC PDUsinto/from MAC PDU. The main functions of the MAC are summarized asfollows.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        transferred to/from the physical layer on transport channels    -   Scheduling information reporting    -   Hybrid automatic repeat request (HARQ) function (error        correction through HARQ)    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   Multimedia broadcast multicast service (MBMS) service        identification    -   Transport format selection    -   padding

The physical layer 220 or 225 performs channel coding and modulation ofupper layer data to configure and transmit OFDM symbols to a radiochannel, or performs demodulation and channel decoding of the OFDMsymbols received on the radio channel to transfer the demodulated andchannel-decoded data to an upper layer.

FIG. 3 is a diagram illustrating the structure of a next-generationmobile communication system according to an embodiment of thedisclosure.

Referring to FIG. 3, as illustrated, a RAN of a next-generation mobilecommunication system (NR or 5G) is composed of a new radio node B (NRgNB or NR ENB) 310 and a new radio core network (NR CN) 305. A new radiouser equipment (NR UE or terminal) 315 accesses to an external networkthrough the NR gNB 310 and the NR CN 305.

In FIG. 3, the NR gNB 310 corresponds to an ENB of the existing LTEsystem. The NR gNB is connected to the NR UE 315 on a radio channel, andthus it can provide a more superior service than the service of theexisting node B. Since all user traffic is serviced on shared channelsin the next-generation mobile communication system, a device thatperforms scheduling through consolidation of status information, such asa buffer state, an available transmission power state, and a channelstate of each UE, is necessary, and the NR gNB 310 takes charge of this.One NR gNB generally controls a plurality of cells. In order toimplement ultrahigh-speed data transmission as compared with theexisting LTE, the NR gNB or cell may have the existing maximum bandwidthor more, and a beamforming technology may be additionally included inconsideration of OFDM as a radio connection technology. Further, an AMCscheme determining a modulation scheme and a channel coding rate tomatch the channel state of the UE is adopted.

The NR CN 305 performs functions of mobility support, bearerconfiguration, and quality of service (QoS) configuration. The NR CN isresponsible for terminal mobility management and various kinds ofcontrol functions, and is connected to a plurality of ENBs. Further, thenext-generation mobile communication system may also be configured tocommunicate with the existing LTE system within region 320, and the NRCN is connected to an MME 325 through a network interface. The MME isconnected to an ENB 330 that is an existing base station.

FIG. 4 is a diagram illustrating a radio protocol structure of anext-generation mobile communication system according to an embodimentof disclosure.

Referring to FIG. 4, in a UE or an NR ENB, a radio protocol of thenext-generation mobile communication system is composed of an NR PDCP405 or 440, an NR RLC 410 or 435, and an NR MAC 415 or 430. The mainfunction of the NR PDCP 405 or 440 may include parts of the followingfunctions.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs    -   PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs    -   Retransmission of PDCP SDUs    -   Ciphering and deciphering    -   Timer-based SDU discard in an uplink

As described above, reordering of the NR PDCP devices may meanreordering of PDCP PDUs received from a lower layer based on PDCPsequence numbers (SNs). The reordering may include delivery of data toan upper layer in the order of reordering, recording of lost PDCP PDUsthrough reordering, status report for the lost PDCP PDUs to atransmission side, and retransmission request for the lost PDCP PDUs.

The main functions of the NR RLC 410 or 435 may include parts of thefollowing functions.

-   -   Transfer of upper layer PDUs    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   Error correction through an ARQ    -   Concatenation, segmentation, and reassembly of RLC SDUs    -   Re-segmentation of RLC data PDUs    -   Reordering of RLC data PDUs    -   Duplicate detection    -   Protocol error detection    -   RLC SDU discard    -   RLC reestablishment

As described above, in-sequence delivery of NR RLC devices may meanin-sequence delivery of RLC SDUs received from a lower layer to an upperlayer. In the case where one RLC SDU is segmented into several RLC SDUsto be received, the in-sequence delivery of the NR RLC devices mayinclude reassembly and delivery of the RLC SDUs. Further, thein-sequence delivery of the NR RLC devices may include reordering of RLCPDUs based on an RLC SN or a PDCP SN, recording of lost RLC PDUs throughreordering, performing of status report for the lost RLC PDUs to atransmission side, and retransmission request for the lost PDCP PDUs.Further, the in-sequence delivery of the NR RLC devices may includein-sequence delivery of only RLC SDUs just before the lost RLC SDU to anupper layer if there is the lost RLC SDU, in-sequence delivery of allRLC SDUs received before a specific timer starts its operation to anupper layer if the timer has expired although there is the lost RLC SDU,or in-sequence delivery of all RLC SDUs received up to now to an upperlayer if the timer has expired although there is the lost RLC SDU.Further, the NR RLC layer may process the RLC PDUs in the order of theirreception (regardless of the order of sequence numbers, in the order oftheir arrival) and may transfer the RLC PDUs to a PDCP device in anout-of-sequence delivery. In case where a packet is segmented, thesegments stored in a buffer or to be received later are received andreconfigured into one complete RLC PDU to be processed and transferredto the PDCP device. The NR RLC layer may not include a concatenationfunction, and the function may be performed by an NR MAC layer or may bereplaced by a multiplexing function of the NR MAC layer.

As described above, the out-of-sequence delivery of the NR RLC devicemeans a function of transferring the RLC SDUs received from a lowerlayer directly to an upper layer in an out-of-sequence delivery. If oneRLC SDU is segmented into several RLC SDUs to be received, theout-of-sequence delivery may include reassembly and delivery of the RLCSDUs, and recording of lost RLC PDUs through storing and ordering theRLC SNs or PDCP SNs of the RLC PDUs.

The NR MAC 415 or 430 may be connected to several NR RLC layer devicesconfigured in one terminal, and the main functions of the NR MAC mayinclude parts of the following functions.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs    -   Scheduling information reporting    -   HARQ function (error correction through HARQ)    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   padding

The NR physical layer 420 or 425 may perform channel coding andmodulation of upper layer data to configure and transmit OFDM symbols toa radio channel, or may perform demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded data to an upper layer.

FIGS. 5A and 5B are diagrams illustrating a data processing structure inan LTE system according to an embodiment of the disclosure.

Referring to FIGS. 5A and 5B, an LTE system performs PDCP-layer andRLC-layer data processing for logical channels. That is, logical channel1 505 and logical channel 2 510 have different PDCP layers and RLClayers, and perform independent data processing. Further, the LTE systemtransfers RLC PDUs generated from RLC layers of the respective logicalchannels to a MAC layer to configure one MAC PDU, and transmits the MACPDU to a receiving end. In the LTE system, the PDCP layer, the RLClayer, and the MAC layer may include the functions as described abovewith reference to FIG. 2, and may perform operations corresponding tothe functions.

In the LTE system, the RLC layer may concatenate PDCP PDUs. Further, inthe LTE system, in a PDCP PDU structure as denoted by reference numeral525, all MAC sub-headers are located in a front portion of the MAC PDU,and a MAC SDU portion is located in the rear portion of the MAC PDU. Dueto that above-described features, in the LTE system, the RLC layer isunable to pre-perform or prepare data processing before a terminalreceives uplink grant.

As shown in FIGS. 5A and 5B, if the uplink grant 530 is received, theterminal generates an RLC PDU by concatenating PDCP PDUs received fromthe PDCP layer to match the uplink grant. After the MAC layer 520receives the uplink grant from a base station, the terminal performslogical channel prioritization (LCP), and divides the uplink grant forthe respective logical channels. That is, the uplink grant 530 is anuplink transmission resource allocated from the base station to the MAClayer 520. If the size of the PDCP PDUs to be concatenated does notmatch the size of the uplink grant, the RLC layer 515 performs asegmentation procedure to make the PDCP PDUs match the uplink grant. Theterminal may perform the above-described procedure for the respectivelogical channels, and each RLC device may configure an RLC header usingthe concatenated PDCP PDUs, and may transmit the completed RLC PDU tothe MAC device.

As described above, the MAC device may configure the RLC PDUs (MAC SDUs)received from the respective RLC layers into one MAC PDU to transmit theMAC PDU to a physical device. If the RLC device performs thesegmentation operation and includes segmentation information in the RLCheader during configuration of the RLC header, it becomes possible toinclude length information of the respective concatenated PDCP PDUs inthe header (this is to reassemble them at a receiving end).

As described above, the LTE system is featured so that the full-scaledata processing of the RLC layer, the MAC layer, and the physical layerstarts from the time when the uplink grant is received.

In the LTE system, the RLC layer may operate in an RLC AM, an RLCunacknowledged mode (UM), and an RLC transparent mode (TM).

In the RLC AM mode, the RLC layer supports an ARQ function, and atransmitting end may receive an RLC status report from the receivingend. Further, the transmitting end may perform retransmission of theunacknowledged RLC PDUs through the status report. Accordingly, anerrorless reliably data transmission can be secured, and thus the RLC AMmode is suitable to services requiring high reliability.

In contrast, in the RLC UM mode, the ARQ function is not supported.Accordingly, in the RLC UM mode, the transmitting end does not receivethe RLC status report, and does not perform the retransmission function.In the RLC UM mode, if the uplink grant is received, the RLC layer ofthe transmitting end serves to concatenate the PDCP PDUs (RLC SDUs)received from an upper layer and to continuously transfer theconcatenated PDCP PDUs to a lower layer. Accordingly, continuous datatransmission without transmission delay becomes possible, and thus theRLC UM mode is useful to services that are sensitive to the transmissiondelay. In the RLC TM mode, the RLC layer directly transmits the PDCPPDUs received from the upper layer to the lower layer without performingany process. That is, in the TM mode of the RLC layer, data from theupper layer is transparently transferred from the RLC layer to the lowerlayer. Accordingly, the RLC TM mode can be usefully used whentransmitting system information or a paging message transmitted througha common channel such as a common control channel (CCCH).

In the disclosure, the PDCP layer and the RLC layer handle an efficientbuffer management method and a retransmission acceleration method, andthus the RLC AM mode and the RLC UM mode excluding the mode in which theRLC layer does not perform any processing, such as the RLC TM mode, willnow be described in detail.

Separate buffer structure of LTE system.

FIG. 6 is a diagram illustrating an efficient buffer management methodsuitable when an LTE system terminal operates in an RLC AM according toan embodiment of the disclosure.

Referring to FIG. 6, a detailed mapping table and correspondingoperations according to the first embodiment for the efficient buffermanagement method when the LTE system terminal operates in the RLC AMmode proposed in the disclosure.

Referring to FIG. 6, a terminal has a first buffer 610 and a secondbuffer 625 for respective logical channels, and a MAC layer has a thirdbuffer 635. The first, second, and third buffers of the logical channelsmay be physically divided buffers, or physically the same, but logicallydivided buffers. In the disclosure, when actually implemented, thebuffers include physically or logically dividable buffer structures, andare divided into, for example, first to third buffers in accordance withtheir roles. Preferably, the first buffer may be a PDCP buffer, thesecond buffer may be an RLC buffer, and the third buffer may be a MACbuffer.

The first buffer 610 may store IP packets (PDCP SDUs) 605 entering intoa PDCP layer, generate a header of the PDCP SDUs, and generate a PDCPPDU 620 by configuring the header together with the PDCP SDUs to storethe PDCP PDU therein. Further, the generated PDCP PDU may be transferredto the second buffer 625.

If an uplink grant is received from the base station, the terminaldistributes the uplink grant to the respective logical channels byreflecting priorities or QoS for the respective logical channels. If theuplink grant is received, the respective logical channels concatenatethe PDCP PDUs (RLC SDUs) in the RLC layer, input length information ofthe respective PDCP PDUs (RLC SDUs) to the header of the RLC PDUs, andconfigure the RLC PDUs 630. If the sizes of the RLC SDUs do notaccurately coincide with each other when the RLC SDUs are concatenatedto the uplink grant, the RLC layer may perform a segmentation operation.If the segmentation is performed with respect to the RLC SDUs, the RLClayer inputs the segmentation information to the header of the RLC PDUs.Further, the RLC layer may transmit the completed RLC PDUs to the MAClayer.

The MAC layer may configure one MAC PDU 640 by multiplexing the RLC PDUsreceived from the different logical channels, and may transmit the MACPDU to the physical layer. Further, for HARQ processing, the MAC layermay store the MAC PDU, and may perform retransmission until anacknowledgement (ACK) is received.

Further detailed contents may be described below with reference to FIG.7.

FIG. 7 is a diagram illustrating a mapping table and a correspondingoperation of an efficient buffer management method when an LTE systemterminal operates in an RLC AM mode according to an embodiment of thedisclosure.

Referring to FIG. 7, if the PDCP PDUs (RLC SDUs) are received from thelayer, the RLC layer may store them in a second buffer 710. Further, theRLC layer may not store the PDCP PDUs (RLC SDUs) in the second buffer710, but may record memory addresses of the PDCP PDUs for reference.

If the size of the uplink grant is received, the RLC layer may configureone RLC PDU through concatenation of the PDCP PDUs (RLC SDUs). Once theRLC PDU is configured as described above, the RLC layer may configure amapping table 735 based on RLC serial numbers and includes memoryaddresses 740 of a second buffer, memory addresses 745 of a firstbuffer, segment information 750, ACK/non-acknowledgment (NACK)information 755, and a PDCP serial number 760. For example, an addressof the second buffer in which the RLC PDU corresponding to RLC serialnumber 1 is stored may be recorded, and a memory address 745 of a firstbuffer for the PDCP PDUs concatenated to record information on the PDCPPDUs concatenated to the RLC PDU may be recorded. The address of thebuffer may be managed as a start link and an end link of the memoryaddress. Further, if the RLC layer has performed a segmentationoperation, segmentation information 750 may be recorded in the mappingtable 735. In the segmentation information, as compared with theoriginal RLC SDUs, if a portion excluding a header of the RLC PDU, thatis, a payload, coincides with the foremost portion of the RLC SDUs, “0”may be recorded as the first bit of an FI field, whereas if the payloaddoes not coincide with the foremost portion, “1” may be recorded as thesecond bit of the FI field. As described above, the segmentationinformation may be recorded. Further, the RLC layer of a transmittingend may identify the ACK/NACK result for the respective RLC serialnumbers after receiving an RLC status report from the RLC layer of areceiving end, and may record the ACK/NACK information 755 for therespective RLC serial numbers. Further, information on what PDCP PDUsare concatenated to the RLC PDUs corresponding to the respective RLCserial numbers may be recorded. That is, information indicating thatPDCP serial numbers 1 and 2 and a part of PDCP serial number 3 areconcatenated to RLC serial number 1 may be recorded. In case ofperforming the segmentation operation in the RLC layer, information onrespective segments may be marked on the last segment. The reason whythe last segment is marked is to identify what PDCP serial numbers canbe considered as an ACK when the ACK is received with respect to acertain RLC serial number. That is, if an ACK is received with respectto RLC serial number 2 after the RLC serial number 2, to which the lastsegment of PDCP serial number 3 and PDCP serial number 4 areconcatenated, is transmitted, the RLC layer may receive an ACK withrespect to the last segment of PDCP serial number 3, and thus mayconsider that it has received the ACK with respect to PDCP serial number3 and PDCP serial number 4.

Whenever uplink grant is received, the RLC layer may make an RLC PDUthrough concatenation and segmentation of PDCP PDUs to transmit the RLCPDU to a lower layer. Further, the RLC layer may transmit and store RLCPDUs in due order, such as 715, 720, and 725, and may record the storedinformation as mapping table information, such as mapping table 735. Ifa NACK is received with respect to RLC serial number 1 in an RLC statusreport received from the RLC layer of the receiving end, the RLC layerof the transmitting end prepares retransmission. In this case, if theuplink grant for the retransmission is smaller than that at thebeginning at operation 715, the RLC layer of the transmitting endperforms re-segmentation, newly configures a header for the segmentedRLC PDUs, transmits the configured RLC PDUs, and separately recordscorresponding information.

The operations of the first buffer and the second buffer are as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the first buffers 610 and 705 throughallocation of memory addresses to the IP packets, and may drive andmanage a PDCP discard timer 615 for each IP packet. A timer value may beconfigured by a network. For example, when the terminal configures anRRC connection, the timer value may be configured by the network throughan RRC message. If the timer expires, the terminal discards the PDCP PDUor the PDCP SDU corresponding to the timer from the first buffer.

If the PDCP PDU corresponding to the timer is sent to the RLC layer, thePDCP layer may transmit a discard indicator corresponding to the PDCPPDU to the RLC layer. The discard indicator may indicate the memoryaddress of the PDCP PDU sent to the RLC layer for the second buffer, thePDCP serial number, or mapping information on the PDCP PDU. Further, ifACK/NACK information on the PDCP PDUs is received from the PDCP layer ofthe receiving end through a PDCP status report, the PDCP layer maydiscard the acknowledged PDCP PDUs from the first buffer, and if anunexpired timer corresponding to the discarded PDCP PDUs exists, it maystop and discard the timer.

If the PDCP PDU corresponding to the discard indicator received from thePDCP layer has not yet become a part of the RLC PDU in the RLC layer orhas not been mapped thereon, the RLC layer discards the correspondinginformation. That is, the RLC layer discards the PDCP PDU (RLC SDU)transferred to and stored in the RLC layer and related information, andmapping information from the second buffer. If the PDCP PDU indicated bythe discard indicator has already become a part of the RLC PDU, the RLClayer does not discard the PDCP PDU and the related information from thesecond buffer. This is because if the PDCP PDU that has already becomethe part of the RLC PDU is discarded, a gap occurs in the RLC serialnumber to cause a transmission delay. That is, the receiving end isunable to discriminate whether the corresponding RLC serial number islost in the transmission process or is discarded by the discardindicator in the transmitting end.

Further, if the RLC status report is received from the RLC layer of thereceiving end, the RLC layer can identify the ACK/NACK result for eachRLC serial number. Further, in case of the acknowledged RLC PDU, the RLClayer may discard the RLC PDU from the second buffer, and may discardthe related mapping information. Further, the RLC layer preparesretransmission for the negatively acknowledged RLC PDU. If the uplinkgrant is sufficient in case where the RLC PDU for the retransmission isstored in the second buffer during performing of the retransmission, theRLC layer may immediately perform the retransmission. Further, if theuplink grant is insufficient, the RLC layer may perform re-segmentationto transmit the RLC PDU at operation 730. If the RLC PDU for theretransmission is not stored in the second buffer, but previouslygenerated information (header information and information onconcatenated PDCP PDUs) and mapping information are recorded, the RLClayer of the transmitting end may dynamically regenerate the RLC PDUbased on this to perform the retransmission.

The RLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table 735, anddetermine the ACK/NACK result for the corresponding PDCP serial number760. If the ACK for the PDCP serial number is identified, the RLC layercan transfer the ACK information for the PDCP serial number to the PDCPlayer. The PDCP layer may identify the ACK information, and may recordthe ACK/NACK information for PDCP serial numbers. The ACK informationfor the PDCP serial numbers may be used during a handover operation.That is, when a terminal handover occurs, the PDCP layer may performretransmission to a target base station of the handover, starting fromthe acknowledged PDCP serial number after the lowest PDCP serial numberin the order of serial numbers. If the network supports a selectiveretransmission during the handover, the PDCP layer may retransmit onlynegatively acknowledged PDCP PDUs to the target base station of thehandover.

FIGS. 8A and 8B are diagrams illustrating the operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode accordingto an embodiment of the disclosure.

Referring to FIG. 8A, if IP packets are received from an upper layer, aterminal PDCP layer operates at operation 801, receives an IP packet atoperation 805, and may store the respective IP packets in a first bufferthrough allocation of memory addresses to the IP packets at operation810. Further, the terminal PDCP layer may drive and manage a PDCPdiscard timer for each IP packet at operation 815. If the timer expires,the terminal discards a PDCP PDU or a PDCP SDU corresponding to thetimer from the first buffer at operation 820. If the PDCP PDUcorresponding to the timer is sent to an RLC layer at operation 825, thePDCP layer may transmit a discard indicator corresponding to the PDCPPDU to the RLC layer at operation 830. The discard indicator mayindicate a memory address of the PDCP PDU sent to the RLC layer for thesecond buffer, the PDCP serial number, or mapping information on thePDCP PDU. Further, if ACK/NACK information on the PDCP PDUs is receivedfrom the PDCP layer of the receiving end through a PDCP status report,the PDCP layer may discard the acknowledged PDCP PDUs from the firstbuffer, and if there exists an unexpired timer corresponding to thediscarded PDCP PDUs, the PDCP layer may stop and discard the timer atoperation 820.

Referring to FIG. 8B, the terminal layer RLC operates at operation 835.If the discard indicator is received from the PDCP layer at operation840, a terminal RLC layer may determine whether to discard theinformation at operation 840. Specifically, if the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU in the RLC layer or has not been mapped thereon at operation845, the terminal RLC layer discards the corresponding information atoperation 855. The contents of the discard indicator are transferred tothe RLC layer, and the terminal RLC layer discards the stored PDCP PDU(RLC SDU), information related to this, and mapping information from thesecond buffer. If the PDCP PDU indicated by the discard indicator hasalready become a part of the RLC PDU (845), the terminal RLC layer 835does not discard the PDCP PDU and the related information from thesecond buffer at operation 850.

If the RLC status report is received from the RLC layer of the receivingend, the RLC layer may identify the ACK/NACK result for each RLC serialnumber. Further, in case of the acknowledged RLC PDU at operation 860,the RLC layer discards the RLC PDU from the second buffer, and discardsthe related mapping information at operation 865. Further, the RLC layerprepares retransmission for the negatively acknowledged RLC PDU atoperation 875. If the uplink grant is sufficient in case where the RLCPDU for the retransmission is stored in the second buffer duringperforming of the retransmission, the RLC layer may immediately performthe retransmission, whereas if the uplink grant is insufficient, the RLClayer may perform re-segmentation to transmit the RLC PDU. If the RLCPDU for the retransmission is not stored in the second buffer, butpreviously generated information (header information and information onconcatenated PDCP PDUs) and mapping information are recorded, the RLClayer may dynamically regenerate the RLC PDU based on this to performthe retransmission.

The RLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table informationat operation 870, and determine the ACK/NACK result for thecorresponding PDCP serial number. If the ACK for the PDCP serial numberis identified, the RLC layer may transfer the ACK information for thePDCP serial number to the PDCP layer. The PDCP layer may identify theACK information, and may record the ACK/NACK information for the PDCPserial numbers.

The first embodiment of an efficient buffer management method suitablewhen the LTE system terminal operates in an RLC AM mode according to thedisclosure has proposed a method in which a PDCP layer manages the firstbuffer independently by a PDCP discard timer, and an RLC layer managesthe second buffer independently by an RLC ACK.

A first embodiment of an efficient buffer management method suitablewhen the LTE system terminal operates in an RLC UM mode according to thedisclosure is as follows.

When operating in the RLC UM mode, the terminal according to thedisclosure has a structure as shown in FIG. 6, and operates in a similarmanner to that as described above with reference to FIG. 7. However,different from the RLC AM mode, an ARQ function is not supported in theRLC UM mode, and thus the retransmission is not performed. Further, theRLC status report is not performed. Accordingly, for the retransmission,it is not necessary to record the already transmitted RLC PDU orinformation related to this, and mapping table information. This is thegreatest difference between the RLC UM mode and the RLC AM mode.

In the disclosure, a first embodiment of a method in which an LTE systemterminal in an RLC UM mode efficiently manages buffers is as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the first buffers 610 and 705 throughallocation of memory addresses to the IP packets. Further, the PDCPlayer may drive and manage a PDCP discard timer for each IP packet. Atimer value may be configured by a network. That is, when the terminalconfigures an RRC connection, the timer value may be configured by thenetwork through an RRC message. If the timer expires, the terminaldiscards the PDCP PDU or the PDCP SDU corresponding to the timer fromthe first buffer.

If the PDCP PDU corresponding to the timer is sent to the RLC layer, thePDCP layer may transmit a discard indicator corresponding to the PDCPPDU to the RLC layer. The discard indicator may indicate the memoryaddress of the PDCP PDU sent to the RLC layer for the second buffer, thePDCP serial number, or mapping information on the PDCP PDU. Further, ifACK/NACK information on the PDCP PDUs is received from the PDCP layer ofthe receiving end through a PDCP status report, the PDCP layer maydiscard the acknowledged PDCP PDUs from the first buffer, and if anunexpired timer corresponding to the discarded PDCP PDUs exists, it maystop and discard the timer.

If the discard indicator is received from the PDCP layer, the RLC layermay discard the information. Specifically, if the PDCP PDU correspondingto the discard indicator has not yet become a part of the RLC PDU in theRLC layer or has not been mapped thereon, the RLC layer discards thecorresponding information. The contents of the discard indicator aretransferred to the RLC layer, and the RLC layer discards the stored PDCPPDU (RLC SDU), information related to this, and mapping information fromthe second buffer. If the PDCP PDU indicated by the discard indicatorhas already become a part of the RLC PDU, the RLC layer does not discardthe PDCP PDU and the related information from the second buffer. This isbecause if the PDCP PDU that has already become the part of the RLC PDUis discarded, a gap occurs in the RLC serial number to cause atransmission delay. That is, the receiving end is unable to discriminatewhether the corresponding RLC serial number is lost in the transmissionprocess or is discarded by the discard indicator in the transmittingend.

Further, the RLC layer may receive uplink grant, and may configure RLCPDUs through concatenation and segmentation of the PDCP PDUs. Further,after completing and transferring the RLC PDUs to the MAC layer, the RLClayer discards the RLC PDUs from the second buffer, and discards therelated information and the mapping information. Accordingly, in the RLCUM mode, the RLC layer transmits the RLC PDUs, and then discards themtogether with the related information without directly storing them inthe second buffer. This is because the ARQ function is not supported inthe RLC UM mode, and thus it is not necessary to record the informationfor the retransmission.

The first embodiment of an efficient buffer management method suitablewhen the LTE system terminal operates in an RLC UM mode according to thedisclosure has proposed a method in which a PDCP layer manages the firstbuffer independently by a PDCP discard timer, and an RLC layer managesthe second buffer independently in accordance with whether to transmitthe RLC PDUs.

FIGS. 9A and 9B are diagrams illustrating the operation of a terminal inwhich an LTE system terminal manages buffers in an RLC UM mode accordingto an embodiment of the disclosure.

Referring to FIG. 9A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 901, the PDCP layer mayreceive an IP packet at operation 905, and the terminal may store therespective IP packets in a first buffer through allocation of memoryaddresses to the IP packets at operation 905. Further, the terminal PDCPlayer may drive and manage a PDCP discard timer for each IP packet atoperation 915. If the timer expires, the terminal discards a PDCP PDU ora PDCP SDU corresponding to the timer from the first buffer at operation920. If the PDCP PDU corresponding to the timer is sent to an RLC layerat operation 925, the PDCP layer may transmit a discard indicatorcorresponding to the PDCP PDU to the RLC layer at operation 930. Thediscard indicator may indicate a memory address of the PDCP PDU sent tothe RLC layer for the second buffer, the PDCP serial number, or mappinginformation on the PDCP PDU. Further, if ACK/NACK information on thePDCP PDUs is received from the PDCP layer of the receiving end through aPDCP status report, the PDCP layer may discard the acknowledged PDCPPDUs from the first buffer, and if there exists an unexpired timercorresponding to the discarded PDCP PDUs, the PDCP layer may stop anddiscard the timer at operation 920.

Referring to FIG. 9B, a terminal RLC layer may operate at operation 935.If the discard indicator is received from the PDCP layer at operation940, a terminal RLC layer 935 may discard the information. Specifically,if the PDCP PDU corresponding to the discard indicator has not yetbecome a part of the RLC PDU in the RLC layer or has not been mappedthereon at operation 945, the terminal RLC layer discards thecorresponding information at operation 955. The contents of the discardindicator are transferred to the RLC layer, and the terminal RLC layerdiscards the stored PDCP PDU (RLC SDU), information related to this, andmapping information from the second buffer. If the PDCP PDU indicated bythe discard indicator has already become a part of the RLC PDU atoperation 945, the terminal RLC layer does not discard the PDCP PDU andthe related information from the second buffer at operation 950.

The RLC layer may receive uplink grant, and may configure RLC PDUsthrough concatenation and segmentation of the PDCP PDUs. Aftercompleting and transferring the RLC PDUs to the MAC layer at operation940, the RLC layer discards the RLC PDUs from the second buffer, anddiscards the related information and the mapping information. That is,in the RLC UM mode, the RLC layer transmits the RLC PDUs, and thendiscards them together with the related information without directlystoring them in the second buffer at operation 960. This is because theARQ function is not supported in the RLC UM mode, and thus it is notnecessary to record the information for the retransmission.

According to the first embodiment of an efficient buffer managementmethod suitable when the LTE system terminal operates in an RLC AM modeand the first embodiment of an efficient buffer management methodsuitable when the LTE system terminal operates in an RLC UM modeproposed in the disclosure, the PDCP layer independently manages thefirst buffer, and the RLC layer independently manages the second buffer.Accordingly, implementation thereof is simple and is not complicated.However, in order to support a high data rate, more optimized buffermanagement method should be considered. For example, if the first bufferis not quickly emptied at a high data rate, a large buffer size may berequired to prevent a buffer overflow due to the high data rate. If asmall timer value is configured in order to prevent the buffer overflow,data may be lost before being transmitted to cause data throughput todeteriorate.

Hereinafter, a second embodiment of an efficient buffer managementmethod suitable when the LTE system terminal operates in an RLC AM modeand a second embodiment of an efficient buffer management methodsuitable when the LTE system terminal operates in an RLC UM mode areproposed.

In the second embodiment of the efficient buffer management methodsuitable when the LTE system terminal operates in the RLC AM mode, thefirst buffer is not independently managed by the PDCP layer, but ismanaged by reflecting the RLC ACK result of the RLC layer. Further, inthe second embodiment of the efficient buffer management method suitablewhen the LTE system terminal operates in the RLC UM mode, the firstbuffer is not independently managed by the PDCP layer, but is managed byreflecting whether to transmit the RLC PDU in the RLC layer.

If the RLC status report is received from the receiving end RLC deviceand the ACK for the RLC PDUs is received in the RLC AM mode, it is notnecessary for the RLC device to have the acknowledged RLC PDUs,information corresponding to this, and mapping table information anyfurther, and it is reasonable for the RLC device to discard them fromthe second buffer. Further, if the PDCP PDUs concatenated to the RLCPDUs having received the ACK exist in the first buffer, even suchinformation is not to be used for the retransmission, and thus it is notnecessary for the RLC layer to have them any further even if the PDCPdiscard timer has not yet expired. Accordingly, in the second embodimentof the efficient buffer management method suitable when the LTE systemterminal according to the disclosure operates in the RLC AM mode, it ispossible for the RLC layer to discard the RLC PDUs having received theRLC ACK from the second buffer. Further, if the RLC layer notifies thePDCP layer of the PDCP PDUs concatenated to the RLC PDUs, thecorresponding PDCP PDUs are discarded from the first buffer, andinformation corresponding to the discarded PDCP PDU and the timer arereleased and discarded.

In contrast, in the RLC UM mode, the ARQ function is not supported, andthus it is not necessary to store the corresponding information afterthe RLC PDUs are transmitted for the retransmission. Accordingly, aftertransmitting the RLC PDUs, the RLC layer does not store thecorresponding RLC PDUs in the second buffer, but discards the relatedinformation if any. Further, once the RLC PDUs are transmitted, it isnot necessary for the RLC layer to have the PDCP PDUs concatenated tothe RLC PDUs any further even if the PDCP discard timer has not yetexpired. Accordingly, in the second embodiment of the efficient buffermanagement method suitable when the LTE system terminal according to thedisclosure operates in the RLC UM mode, the RLC layer does not store thecorresponding RLC PDUs in the second buffer after transmitting the RLCPDUs, but discards the related information if any. Further, if theinformation on the PDCP PDUs concatenated to the RLC PDUs is sent to thePDCP layer, the PDCP layer immediately discards the information on thePDCP PDUs from the first buffer even if the PDCP discard timer has notyet expired.

FIGS. 10A and 10B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode accordingto an embodiment of the disclosure.

Referring to FIG. 10A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 1001, the PDCP layer mayreceive an IP packet at operation 1005, and the terminal may store therespective IP packets in a first buffer through allocation of memoryaddresses to the IP packets at operation 1005. Further, the terminalPDCP layer may drive and manage a PDCP discard timer for each IP packetat operation 1015. If the timer expires, the terminal discards a PDCPPDU or a PDCP SDU corresponding to the timer from the first buffer atoperation 1020. If the PDCP PDU corresponding to the timer is sent to anRLC layer at operation 1025, the PDCP layer may transmit a discardindicator corresponding to the PDCP PDU to the RLC layer at operation1030. The discard indicator may indicate a memory address of the PDCPPDU sent to the RLC layer for the second buffer, the PDCP serial number,or mapping information on the PDCP PDU.

Further, if ACK/NACK information on the PDCP PDUs is received from thePDCP layer of the receiving end through a PDCP status report, the PDCPlayer may discard the acknowledged PDCP PDUs from the first buffer.Further, if there exists an unexpired timer corresponding to thediscarded PDCP PDUs, the PDCP layer may stop and discard the timer atoperation 1020. Further, the PDCP layer may receive from the RLC layerinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK. Since the PDCP PDUs mean that they have beensuccessfully transferred to the receiving end, it is not necessary tostore them in the first buffer any more, and the PDCP layer discardsthem, the corresponding information, and the mapping table information.If there exists an unexpired timer, the PDCP layer may stop and discardthe timer at operation 1020. In case of managing the first buffer basedon the RLC ACK, it is significant to differently manage the first bufferin accordance with the PDCP layer operation of the terminal during ahandover.

As a first case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should retransmit thePDCP PDUs to a target base station of the handover again after thelowest PDCP serial number successfully transferred in order up to nowduring the handover. In this case, if information on the PDCP PDUsconcatenated to the RLC PDUs having received the RLC ACK is received,the PDCP layer should store the lowest PDCP serial number havingreceived all the ACKs in the order of PDCP serial numbers. Further, withrespect to the PDCP serial numbers that are higher than the lowest PDCPserial number, the PDCP layer should not discard them even if the RLClayer has received the RLC ACK. That is, the PDCP PDUs of which thesuccessful transfer has been identified based on the RLC ACK can bediscarded only in the order of their PDCP serial numbers. For example,even if it is identified that PDCP serial numbers 1, 2, 3, 4, 5, 9, and10 have been successfully transferred from the RLC ACK of the RLC layer,only the PDCP serial numbers 1, 2, 3, 4, and 5 can be discarded from thefirst buffer together with information related to the corresponding PDCPPDUs and mapping information.

As a second case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should selectivelyretransmit the PDCP PDUs having not been successfully transferred up tonow to the target base station of the handover. In this case, ifinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK is received, the PDCP layer may discard theinformation corresponding to the PDCP PDUs and the mapping informationfrom the first buffer, and may separately store the information on thePDCP serial numbers having received the ACK in order to use theinformation during the handover.

Referring to FIG. 10B, the terminal RLC layer operates at operation1035. If the discard indicator is received from the PDCP layer atoperation 1040, a terminal RLC layer may discard the informationcorresponding to the discard indicator. Specifically, if the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU in the RLC layer or has not been mapped thereon at operation1045, the terminal RLC layer discards the corresponding information atoperation 1055. The contents of the discard indicator are transferred tothe RLC layer, and the terminal RLC layer discards the stored PDCP PDU(RLC SDU), information related to this, and mapping information from thesecond buffer. If the PDCP PDU indicated by the discard indicator hasalready become the part of the RLC PDU (1045), the terminal RLC layerdoes not discard the PDCP PDU and the related information from thesecond buffer at operation 1050.

If the RLC status report is received from the RLC layer of the receivingend at operation 1040, the RLC layer may identify the ACK/NACK resultfor each RLC serial number. Further, in case of the acknowledged RLC PDUat operation 1060, the RLC layer discards the RLC PDU from the secondbuffer, and discards the related mapping information at operation 1065.The RLC layer prepares retransmission for the negatively acknowledgedRLC PDU at operation 1075. If the uplink grant is sufficient in casewhere the RLC PDU for the retransmission is stored in the second bufferduring performing of the retransmission, the RLC layer may immediatelyperform the retransmission, whereas if the uplink grant is insufficient,the RLC layer may perform re-segmentation to transmit the RLC PDU. Ifthe RLC PDU for the retransmission is not stored in the second buffer,but previously generated information (header information and informationon concatenated PDCP PDUs) and mapping information are recorded, the RLClayer may dynamically regenerate the RLC PDU based on this to performthe retransmission.

The RLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table informationat operation 1070, and determine the ACK/NACK result for thecorresponding PDCP serial number. If the ACK for the PDCP serial numberis identified, the RLC layer may transfer the ACK information for thePDCP serial number to the PDCP layer. The PDCP layer may identify theACK information, and may use the ACK information to discard thecorresponding PDCP PDUs from the first buffer.

Accordingly, in the second embodiment of the efficient buffer managementmethod suitable when the LTE system terminal operates in the RLC AMmode, it is featured that the RLC layer discards the RLC PDUs havingreceived the RLC ACK from the second buffer, notifies the PDCP layer ofthe PDCP PDUs concatenated to the RLC PDUs, discards the correspondingPDCP PDUs from the first buffer, and releases and discards thecorresponding information and timer. Accordingly, the buffer can beefficiently managed even with a small-sized buffer to rapidly empty thefirst buffer, and thus efficiency can be maximized.

FIGS. 11A and 11B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC UM mode accordingto an embodiment of the disclosure.

Referring to FIG. 11A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 1101, a PDCP layer mayreceive an IP packet at operation 1105, the terminal may store therespective IP packets in a first buffer through allocation of memoryaddresses to the IP packets at operation 1110, and may drive and managea PDCP discard timer for each IP packet at operation 1115. If the timerexpires, the terminal discards a PDCP PDU or a PDCP SDU corresponding tothe timer from the first buffer at operation 1120. If the PDCP PDUcorresponding to the timer is sent to an RLC layer at operation 1125,the PDCP layer may transmit a discard indicator corresponding to thePDCP PDU to the RLC layer at operation 1130. The discard indicator mayindicate a memory address of the PDCP PDU sent to the RLC layer for thesecond buffer, the PDCP serial number, or mapping information on thePDCP PDU. Further, if ACK/NACK information on the PDCP PDUs is receivedfrom the PDCP layer of the receiving end through a PDCP status report,the PDCP layer may discard the acknowledged PDCP PDUs from the firstbuffer, and if there exists an unexpired timer corresponding to thediscarded PDCP PDUs, the PDCP layer may stop and discard the timer atoperation 1120. Further, if the RLC PDU is transmitted from the RLClayer and the RLC layer transfers to the PDCP layer information on thePDCP PDUs concatenated to the transmitted RLC PDUs, the PDCP layer maydiscard the information on the transmitted PDCP PDUs from the firstbuffer, and if the corresponding timer has not expired, the PDCP layermay release and discard the timer.

Referring to FIG. 11B, a terminal RLC layer may operate at operation1135. If the discard indicator is received from the PDCP layer atoperation 1140, a terminal RLC layer 1135 may discard the informationcorresponding to the discard indicator. Specifically, if the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU in the RLC layer or has not been mapped thereon at operation1145, the terminal RLC layer discards the corresponding information atoperation 1155. The contents of the discard indicator are transferred tothe RLC layer, and the terminal RLC layer discards the stored PDCP PDU(RLC SDU), information related to this, and mapping information from thesecond buffer. If the PDCP PDU indicated by the discard indicator hasalready become a part of the RLC PDU at operation 1145, the terminal RLClayer does not discard the PDCP PDU and the related information from thesecond buffer at operation 1150.

The RLC layer may receive uplink grant, and may configure RLC PDUsthrough concatenation and segmentation of the PDCP PDUs. Aftercompleting and transferring the RLC PDUs to the MAC layer at operation1140, the RLC layer discards the RLC PDUs from the second buffer, anddiscards the related information and the mapping information atoperation 1160. That is, in the RLC UM mode, the RLC layer transmits theRLC PDUs, and then discards them together with the related informationwithout directly storing them in the second buffer. This is because theARQ function is not supported in the RLC UM mode, and thus it is notnecessary to record the information for the retransmission. Further, theRLC layer may determine and transfer to the PDCP layer information onthe PDCP PDUs concatenated to the transmitted RLC PDUs, and may use theinformation to manage the first buffer at operation 1165.

Accordingly, in the second embodiment of the efficient buffer managementmethod suitable when the LTE system terminal operates in the RLC UMmode, it is featured that after transmitting the RLC PDUs, the RLC layerdoes not store the corresponding RLC PDUs in the second buffer, butdiscards the related information if any, and transmits to the PDCP layerinformation on the PDCP PDUs concatenated to the RLC PDUs. Even if thePDCP timer has not expired, the PDCP layer immediately discards theinformation on the PDCP PDUs from the first buffer.

Shared buffer structure of LTE system.

FIG. 12 is a diagram illustrating mapping table and a buffer managementmethod suitable when an LTE system terminal operates in an RLC AM modeaccording to an embodiment of the disclosure, and shows a detailedmapping table and a corresponding operation.

Referring to FIG. 12, a terminal has a fourth buffer for each logicalchannel. The fourth buffer may be an integrated buffer in which thefirst buffer and the second buffer as illustrated in FIGS. 6 and 7 areshared to be used. Preferably, the fourth buffer may be a shared buffer.Accordingly, through the use of the shared buffer, it is possible tomanage the buffer more efficiently. The fourth buffers of the logicalchannels may be physically divided buffers, or physically the same, butlogically divided buffers. In the disclosure, when actually implemented,the buffers include physically or logically dividable buffer structures.

The fourth buffer 1205 may store IP packets (PDCP SDUs) 1210 enteringinto a PDCP layer, generate a header of the PDCP SDUs, and make a PDCPPDU 1215 by configuring the header together with the PDCP SDUs to storethe generated PDCP PDU therein. Further, if an uplink grant is receivedfrom the base station, the terminal distributes the uplink grant to therespective logical channels by reflecting the priority or QoS for eachlogical channel. If the uplink grant is received as described above, theRLC layer concatenates the PDCP PDUs (RLC SDUs) in the fourth buffer tothe respective logical channels, inputs length information of therespective PDCP PDUs (RLC SDUs) to a header of the RLC PDUs, anddynamically configures the RLC PDUs 630. If the sizes of the RLC SDUs donot accurately coincide with the uplink grant when the RLC SDUs areconcatenated to the uplink grant, the RLC layer may perform asegmentation operation. If the segmentation is performed with respect tothe RLC SDUs, the RLC layer inputs the segmentation information to theheader of the RLC PDUs. Further, the RLC layer may transmit thecompleted RLC PDUs to the MAC layer.

Further, the MAC layer may configure one MAC PDU by multiplexing the RLCPDUs received from different logical channels, and may transmit the MACPDU to the physical layer. Further, for HARQ processing, the MAC layermay store the MAC PDU, and may perform retransmission thereof until anACK is received.

If the size of the uplink grant is known, the fourth buffer mayconfigure one RLC PDU through concatenation of the PDCP PDUs (RLC SDUs).In the third embodiment of the efficient buffer management methodsuitable when the LTE system terminal operates in the RLC AM modeproposed in the disclosure, the RLC PDU may not be stored for theretransmission after the RLC PDU is configured and transmitted.Accordingly, in the third embodiment, memory addresses of theconcatenated PDCP PDUs during configuration of the RLC PDU in the fourthbuffer, segmentation information, and header information are recorded ina mapping table, and if the retransmission is necessary, the RLC PDU isdynamically reconfigured and transmitted with reference to the recordedinformation.

Once the RLC PDU is configured as described above, the RLC layer mayconfigure a mapping table 1220 based on RLC serial numbers. For example,in order to record information on the PDCP PDUs concatenated to the RLCPDUs corresponding to RLC serial number 1, the RLC layer may record amemory address of the fourth buffer for the concatenated PDCP PDUs. Theaddress of the buffer may be composed of a start link and an end link ofthe memory address. Further, if the RLC layer has performed asegmentation operation, segmentation information may be recorded. In thesegmentation information, as compared with the original RLC SDUs, if aportion excluding a header of the RLC PDU, that is, a payload, coincideswith the foremost portion of the RLC SDUs, “0” may be recorded as thefirst bit of an FI field, whereas if the payload does not coincide withthe foremost portion, “1” may be recorded as the first bit of the FIfield. As compared with the original RLC SDUs, if the payload coincideswith the rearmost portion of the RLC SDUs, “0” may be recorded as thesecond bit of the FI field, whereas if the payload does not coincidewith the rearmost portion, “1” may be recorded as the second bit of theFI field. The RLC layer may record the segmentation information asdescribed above.

Further, the RLC layer of a transmitting end may identify the ACK/NACKresult for the respective RLC serial numbers after receiving an RLCstatus report from the RLC layer of a receiving end, and may record theACK/NACK for the respective RLC serial numbers. Further, the RLC layermay record information on what PDCP PDUs are concatenated to the RLCPDUs corresponding to the respective RLC serial numbers. That is,information indicating that PDCP serial numbers 1 and 2 and a part ofPDCP serial number 3 are concatenated to RLC serial number 1 may berecorded. In case of performing the segmentation operation in the RLClayer, information on respective segments may be marked on the lastsegment.

The reason why the last segment is marked is to identify what PDCPserial numbers can be considered as an ACK when the ACK is received withrespect to a certain RLC serial number. That is, if an ACK is receivedwith respect to RLC serial number 2 after the RLC serial number 2, towhich the last segment of PDCP serial number 3 and PDCP serial number 4are concatenated, is transmitted, the RLC layer may receive an ACK withrespect to the last segment of PDCP serial number 3, and thus mayconsider that it has received the ACK with respect to PDCP serial number3 and PDCP serial number 4.

Whenever the uplink grant is received, the RLC layer may make an RLC PDUthrough concatenation and segmentation of PDCP PDUs to transmit the RLCPDU to a lower layer. Further, the RLC layer may transmit and store RLCPDUs in due order. For example, the RLC layer may record the informationas mapping table information, such as mapping table 1220. If a NACK isreceived with respect to RLC serial number 1 in an RLC status reportreceived from the RLC layer of the receiving end, the RLC layer preparesretransmission. In this case, if the uplink grant for the retransmissionis smaller than that at the beginning, the RLC layer performsre-segmentation, newly configures a header for the segmented RLC PDUs,and transmits the configured RLC PDUs. Further, the RLC layer mayseparately record information on the retransmitted RLC PDU at operation1225.

The operation of the fourth buffer is as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the fourth buffer through allocation ofmemory addresses to the respective IP packets. Further, the PDCP layermay drive and manage a PDCP discard timer for each IP packet. A timervalue may be configured by a network. That is, when the terminalconfigures an RRC connection, the timer value may be configured by thenetwork through an RRC message. If the timer expires, the terminaldiscards the PDCP PDU or the PDCP SDU corresponding to the timer fromthe fourth buffer. If the PDCP PDU corresponding to the timer is sent tothe RLC layer, the PDCP layer may transmit a discard indicatorcorresponding to the PDCP PDU to the RLC layer. The discard indicatormay indicate the PDCP PDU serial number transmitted to the RLC layer ormapping information for the PDCP PDU. Further, if ACK/NACK informationon the PDCP PDUs is received from the PDCP layer of the receiving endthrough a PDCP status report, the PDCP layer may discard theacknowledged PDCP PDUs from the fourth buffer, and if an unexpired timercorresponding to the discarded PDCP PDUs exists, it may stop and discardthe timer. Further, the PDCP layer may receive from the RLC layerinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK. Since the PDCP PDUs mean that they have beensuccessfully transferred to the receiving end, it is not necessary tostore them in the fourth buffer any more. Accordingly, the informationstored in the fourth buffer may be discarded. Specifically, informationcorresponding to the PDCP PDUs successfully transferred to the receivingend and mapping table information may be discarded, and if there existsan unexpired timer, the timer may also be stopped and discarded. In caseof managing the fourth buffer based on the RLC ACK, it is significant todifferently manage the fourth buffer in accordance with the PDCP layeroperation of the terminal during a handover.

As a first case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should retransmit thePDCP PDUs to a target base station of the handover again after thelowest PDCP serial number successfully transferred in order up to nowduring the handover. In this case, if information on the PDCP PDUsconcatenated to the RLC PDUs having received the RLC ACK is received,the PDCP layer should store the lowest PDCP serial number havingreceived all the ACKs in the order of PDCP serial numbers. Further, withrespect to the PDCP serial numbers that are higher than the lowest PDCPserial number, the PDCP layer should not discard them even if the RLClayer has received the RLC ACK. That is, the PDCP PDUs of which thesuccessful transfer has been identified based on the RLC ACK can bediscarded only in the order of their PDCP serial numbers. For example,even if it is identified that PDCP serial numbers 1, 2, 3, 4, 5, 9, and10 have been successfully transferred from the RLC ACK of the RLC layer,only the PDCP serial numbers 1, 2, 3, 4, and 5 can be discarded from thefourth buffer together with information related to the correspondingPDCP PDUs and mapping information.

As a second case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should selectivelyretransmit the PDCP PDUs having not been successfully transferred up tonow to the target base station of the handover. In this case, ifinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK is received, the PDCP layer may discard theinformation corresponding to the PDCP PDUs and the mapping informationfrom the fourth buffer, and may separately store the information on thePDCP serial numbers having received the ACK in order to use theinformation during the handover.

If the discard indicator is received from the PDCP layer, the RLC layermay discard the corresponding information in a state where the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU or has not been mapped thereon. Specifically, the RLC layerdiscards information related to the PDCP PDU (RLC SDU) transferred toand stored in the RLC layer and mapping information. If the PDCP PDUindicated by the discard indicator has already become the part of theRLC PDU, the RLC layer does not discard the PDCP PDU and the relatedinformation. This is because if the PDCP PDU that has already become thepart of the RLC PDU is discarded, a gap occurs in the RLC serial numberto cause a transmission delay. The receiving end is unable todiscriminate whether the corresponding RLC serial number is lost in thetransmission process or is discarded by the discard indicator in thetransmitting end.

If the RLC status report is received from the RLC layer of the receivingend, the RLC layer may identify the ACK/NACK result for each RLC serialnumber, and in case of the acknowledged RLC PDU, the RLC layer discardsthe mapping information related to this. The RLC layer preparesretransmission for the negatively acknowledged RLC PDU. If the uplinkgrant is sufficient in case where the retransmission is performed, theRLC layer may dynamically regenerate and retransmit the RLC PDU usingthe mapping table information, whereas if the uplink grant isinsufficient, the RLC layer may perform re-segmentation at operation1225 and dynamically regenerate and transmit the RLC PDUs.

The RLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table information1220, and determine the ACK/NACK result for the corresponding PDCPserial number. If the ACK for the PDCP serial number is identified, theRLC layer may transfer the ACK information for the PDCP serial number tothe PDCP layer. The PDCP layer may identify the ACK information, and mayrecord the ACK/NACK information for each PDCP serial number. The ACKinformation for the PDCP serial numbers may be used during a handover.When a terminal handover occurs, the PDCP layer may performretransmission to a target base station of the handover, starting fromthe PDCP serial number after the lowest PDCP serial number havingreceived all the ACKs in the order of serial numbers. If the networksupports a selective retransmission during the handover, the PDCP layermay retransmit only negatively acknowledged PDCP PDUs to the target basestation of the handover.

In a fourth embodiment of an efficient buffer management method suitablewhen an LTE system terminal operates in an RLC AM mode according to thedisclosure, it is featured that the fourth buffer is not independentlymanaged by the PDCP layer, but is managed by reflecting the RLC ACKresult of the RLC layer. Further, in a fourth embodiment of an efficientbuffer management method suitable when the LTE system terminal operatesin an RLC UM mode, it is featured that the fourth buffer is notindependently managed by the PDCP layer, but is managed by reflectingwhether to transmit the RLC PDU in the RLC layer.

If an RLC status report is received from the receiving end RLC deviceand an ACK for RLC PDUs is received in an RLC AM mode, it is notnecessary for the RLC device to have information corresponding to theacknowledged RLC PDUs and mapping table information any further, and itis reasonable for the RLC device to discard them from the fourth buffer.Further, if the PDCP PDUs concatenated to the RLC PDUs having receivedthe ACK exist in the fourth buffer, even such information is not to beused for retransmission, and thus it is not necessary for the RLC layerto have them any further even if a PDCP discard timer has not yetexpired.

Accordingly, in the third embodiment of the efficient buffer managementmethod suitable when the LTE system terminal according to the disclosureoperates in the RLC AM mode, it is featured that the RLC layer discardsinformation on the RLC PDUs having received the RLC ACK from a mappingtable, notifies the PDCP layer of the PDCP PDUs concatenated to the RLCPDUs, discards the corresponding PDCP PDUs from the fourth buffer,releases and discards the corresponding information and timer.

A third embodiment of an efficient buffer management method suitablewhen an LTE system terminal having the structure as shown in FIG. 12operates in an RLC UM mode is as follow.

When operating in the RLC UM mode, the terminal according to thedisclosure has the structure as shown in FIG. 12, and operates in asimilar manner to that as described above with reference to FIG. 12.However, different from the RLC AM mode, an ARQ function is notsupported in the RLC UM mode, and thus retransmission is not performed.Further, an RLC status report is not performed. Accordingly, it is notnecessary to record already transmitted RLC PDUs or related information,and mapping table information for the retransmission. This is thegreatest difference between the RLC UM mode and the RLC AM mode.

In the disclosure, a third embodiment of a method in which an LTE systemterminal in an RLC UM mode efficiently manages buffers is as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the fourth buffer 1205 through allocationof memory addresses to the IP packets. Further, the PDCP layer may driveand manage a PDCP discard timer for each IP packet. A timer value may beconfigured by a network. For example, when the terminal configures anRRC connection, the timer value may be configured by the network throughan RRC message. If the timer expires, the terminal discards the PDCP PDUor the PDCP SDU corresponding to the timer from the fourth buffer. Ifthe PDCP PDU corresponding to the timer is sent to the RLC layer, thePDCP layer may transmit a discard indicator corresponding to the PDCPPDU to the RLC layer. The discard indicator may indicate the memoryaddress of the PDCP PDU sent to the RLC layer or mapping information onthe PDCP PDU.

Further, if ACK/NACK information on the PDCP PDUs is received from thePDCP layer of the receiving end through a PDCP status report, the PDCPlayer may discard the acknowledged PDCP PDUs from the fourth buffer, andif an unexpired timer corresponding to the discarded PDCP PDUs exists,it may stop and discard the timer.

If the discard indicator is received from the PDCP layer, the RLC layermay discard the information corresponding to the discard indicator.Specifically, if the PDCP PDU corresponding to the discard indicator hasnot yet become a part of the RLC PDU in the RLC layer or has not beenmapped thereon, the RLC layer discards the corresponding information.The contents of the discard indicator are transferred to the RLC layer,and the RLC layer discards information related to the stored PDCP PDU(RLC SDU) and mapping information.

If the PDCP PDU indicated by the discard indicator has already become apart of the RLC PDU, the RLC layer does not discard the relatedinformation. This is because if the PDCP PDU that has already become thepart of the RLC PDU is discarded, a gap occurs in the RLC serial numberto cause a transmission delay. That is, the receiving end is unable todiscriminate whether the corresponding RLC serial number is lost in thetransmission process or is discarded by the discard indicator in thetransmitting end.

The RLC layer may receive uplink grant, and may configure RLC PDUsthrough concatenation and segmentation of the PDCP PDUs. Further, aftercompleting and transferring the RLC PDUs to a MAC layer, the RLC layerdiscards information related to the RLC PDUs and mapping information. Inthe RLC UM mode, the RLC layer transmits the RLC PDUs, and then discardsthem together with the related information without storing them. This isbecause the ARQ function is not supported in the RLC UM mode, and thusit is not necessary to record the information for the retransmission.

In the RLC UM mode, the ARQ function is not supported, and thus it isnot necessary to store the corresponding information after the RLC PDUsare transmitted for the retransmission. Accordingly, after transmittingthe RLC PDUs, the RLC layer does not store the corresponding RLC PDUs inthe fourth buffer, but discards the related information if any. Further,once the RLC PDUs are transmitted, it is not necessary for the RLC layerto have the PDCP PDUs concatenated to the RLC PDUs any further even ifthe PDCP discard timer has not yet expired.

Accordingly, in the third embodiment of the efficient buffer managementmethod suitable when the LTE system terminal according to the disclosureoperates in the RLC UM mode, the RLC layer may not store thecorresponding RLC PDUs in the fourth buffer and the mapping table aftertransmitting the RLC PDUs. Further, if the related information exists,the RLC layer discards the information, and may transmit information onthe PDCP PDUs concatenated to the RLC PDUs to the PDCP layer. If theinformation on the PDCP PDUs is received, the PDCP layer immediatelydiscards the information on the PDCP PDUs from the fourth buffer even ifthe PDCP discard timer has not yet expired.

FIGS. 13A and 13B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC AM mode accordingto an embodiment of the disclosure.

Referring to FIG. 13A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 1301, the PDCP layer mayreceive an IP packet at operation 1305, and the terminal may store therespective IP packets in a fourth buffer through allocation of memoryaddresses to the IP packets at operation 1310. Further, the terminalPDCP layer may drive and manage a PDCP discard timer for each IP packetat operation 1315. If the timer expires, the terminal discards a PDCPPDU or a PDCP SDU corresponding to the timer from the first buffer atoperation 1320. If the PDCP PDU corresponding to the timer istransmitted to an RLC layer at operation 1325, the PDCP layer maytransmit a discard indicator corresponding to the PDCP PDU to the RLClayer at operation 1330. The discard indicator may indicate the PDCP PDUserial number transmitted to the RLC layer, or mapping information onthe PDCP PDU.

Further, if ACK/NACK information on the PDCP PDUs is received from thePDCP layer of the receiving end through a PDCP status report, the PDCPlayer may discard the acknowledged PDCP PDUs from the fourth buffer.Further, if there exists an unexpired timer corresponding to thediscarded PDCP PDUs, the PDCP layer may stop and discard the timer atoperation 1320. Further, the PDCP layer may receive from the RLC layerinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK. Since the PDCP PDUs mean that they have beensuccessfully transferred to the receiving end, it is not necessary tostore them in the fourth buffer any more, and the PDCP layer may discardthem.

Further, the PDCP layer discards information corresponding to thediscarded PDCP PDU and mapping table information. If there exists anunexpired timer, the PDCP layer may stop and discard the timer atoperation 1320. In case of managing the fourth buffer based on the RLCACK, it is significant to differently manage the fourth buffer inaccordance with the PDCP layer operation of the terminal during ahandover.

As a first case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should retransmit thePDCP PDUs to a target base station of the handover again after thelowest PDCP serial number successfully transferred in order up to nowduring the handover. In this case, if information on the PDCP PDUsconcatenated to the RLC PDUs having received the RLC ACK is received,the PDCP layer should store the lowest PDCP serial number havingreceived all the ACKs in the order of PDCP serial numbers. Further, withrespect to the PDCP serial numbers that are higher than the lowest PDCPserial number, the PDCP layer should not discard them even if the RLClayer has received the RLC ACK. That is, the PDCP PDUs of which thesuccessful transfer has been identified based on the RLC ACK can bediscarded only in the order of their PDCP serial numbers. For example,even if it is identified that PDCP serial numbers 1, 2, 3, 4, 5, 9, and10 have been successfully transferred from the RLC ACK of the RLC layer,only the PDCP serial numbers 1, 2, 3, 4, and 5 can be discarded from thefourth buffer together with information related to the correspondingPDCP PDUs and mapping information.

As a second case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should selectivelyretransmit the PDCP PDUs having not been successfully transferred up tonow to the target base station of the handover. In this case, ifinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK is received, the PDCP layer may discard theinformation corresponding to the PDCP PDUs and the mapping informationfrom the fourth buffer, and may separately store the information on thePDCP serial numbers having received the ACK in order to use theinformation during the handover.

Referring to FIG. 13B, a terminal RLC layer may operate at operation1335. If the discard indicator is received from the PDCP layer atoperation 1340, a terminal RLC layer may discard the informationcorresponding to the discard indicator. Specifically, if the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU in the RLC layer or has not been mapped thereon at operation1345, the terminal RLC layer discards the corresponding information atoperation 1355. The contents of the discard indicator are transferred tothe RLC layer, and the terminal RLC layer discards information relatedto the stored PDCP PDU (RLC SDU) and mapping information. If the PDCPPDU indicated by the discard indicator has already become the part ofthe RLC PDU at operation 1345, the terminal RLC layer does not discardthe information related to the PDCP PDU at operation 1350.

If the RLC status report is received from the RLC layer of the receivingend at operation 1340, the RLC layer may identify the ACK/NACK resultfor each RLC serial number. Further, in case of the acknowledged RLC PDUat operation 1360, the RLC layer discards the related mappinginformation at operation 1365. The RLC layer prepares retransmission forthe negatively acknowledged RLC PDU at operation 1375. If the uplinkgrant for the retransmission is sufficient during performing of theretransmission, the RLC layer may dynamically regenerate and retransmitthe RLC PDU based on the mapping information for the RLC PDU and headerinformation. Further, if the uplink grant is insufficient, the RLC layermay perform re-segmentation at operation 730 to dynamically generate andtransmit the RLC PDUs. The RLC layer may identify the result of theACK/NACK for the RLC serial number through the RLC status report,identify mapping table information at operation 1370, and determine theACK/NACK result for the corresponding PDCP serial number. If the ACK forthe PDCP serial number is identified, the RLC layer may transfer the ACKinformation for the PDCP serial number to the PDCP layer. The PDCP layermay identify the ACK information, and may use the ACK information todiscard the corresponding PDCP PDUs from the fourth buffer.

Accordingly, in the third embodiment of the efficient buffer managementmethod suitable when the LTE system terminal operates in the RLC AM modeaccording to the disclosure, the RLC layer can discard information onthe RLC PDUs having received the RLC ACK and mapping table information.Further, if the RLC layer notifies the PDCP layer of the PDCP PDUsconcatenated to the RLC PDUs, the PDCP layer discards the correspondingPDCP PDUs from the fourth buffer, and releases and discards thecorresponding information and timer. Accordingly, the buffer can beefficiently managed even with a small-sized buffer to rapidly empty thefourth buffer, and thus efficiency can be maximized.

FIGS. 14A and 14B are diagrams illustrating operation of a terminal inwhich an LTE system terminal manages buffers in an RLC UM mode accordingto an embodiment disclosure.

Referring to FIG. 14A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 1401, the terminal PDCPlayer may receive an IP packet at operation 1405, and the terminal maystore the respective IP packets in a fourth buffer through allocation ofmemory addresses to the IP packets at operation 1410. Further, theterminal PDCP layer may drive and manage a PDCP discard timer for eachIP packet at operation 1415. If the timer expires, the terminal discardsa PDCP PDU or a PDCP SDU corresponding to the timer from the fourthbuffer at operation 1420. If the PDCP PDU corresponding to the timer istransmitted to an RLC layer at operation 1425, the PDCP layer maytransmit a discard indicator corresponding to the PDCP PDU to the RLClayer at operation 1430. The discard indicator may indicate a PDCP PDUserial number transmitted to the RLC layer or mapping information on thePDCP PDU.

Further, if ACK/NACK information on the PDCP PDUs is received from thePDCP layer of the receiving end through a PDCP status report, the PDCPlayer may discard the acknowledged PDCP PDUs from the fourth buffer, andif there exists an unexpired timer corresponding to the discarded PDCPPDUs, the PDCP layer may stop and discard the timer at operation 1420.Further, if the RLC PDU is transmitted from the RLC layer and the RLClayer transfers to the PDCP layer information on the PDCP PDUsconcatenated to the transmitted RLC PDUs, the PDCP layer may discard theinformation on the transmitted PDCP PDUs from the fourth buffer, and ifthe corresponding timer has not expired, the PDCP layer may release anddiscard the timer.

Referring to FIG. 14B, a terminal RLC layer may operate at operation1435. If the discard indicator is received from the PDCP layer atoperation 1440, the terminal RLC layer 1435 may discard the informationcorresponding to the discard indicator is received at operation 1440.Specifically, if the PDCP PDU corresponding to the discard indicator hasnot yet become a part of the RLC PDU in the RLC layer or has not beenmapped thereon at operation 1445, the terminal RLC layer discards thecorresponding information at operation 1455. The contents of the discardindicator are transferred to the RLC layer, and the terminal RLC layerdiscards information related to the stored PDCP PDU (RLC SDU) andmapping information. If the PDCP PDU indicated by the discard indicatorhas already become a part of the RLC PDU at operation 1445, the terminalRLC layer does not discard the information related to the PDCP PDU atoperation 1450.

The RLC layer may receive uplink grant, and may configure RLC PDUsthrough concatenation and segmentation of the PDCP PDUs. Aftercompleting and transferring the RLC PDUs to a MAC layer at operation1440, the RLC layer discards information related to the RLC PDUs andmapping information at operation 1460. In the RLC UM mode, the RLC layertransmits the RLC PDUs, and then discards the related information, ifany, without storing them. This is because the ARQ function is notsupported in the RLC UM mode, and thus it is not necessary to record theinformation for the retransmission. Further, the RLC layer may determineand transfer to the PDCP layer information on the PDCP PDUs concatenatedto the transmitted RLC PDUs, and may use the information to manage thefourth buffer at operation 1465.

Accordingly, in the third embodiment of the efficient buffer managementmethod suitable when the LTE system terminal operates in the RLC UMmode, the RLC layer transmits the RLC PDUs, and then discards relatedinformation, if any, without storing the corresponding RLC PDUs.Further, the RLC layer may transmit to the PDCP layer information on thePDCP PDUs concatenated to the RLC PDUs. Even if the PDCP timer has notexpired, the PDCP layer immediately discards the information on the PDCPPDUs from the fourth buffer.

Buffer structure of next-generation mobile communication system andretransmission acceleration.

In the fore portion of the disclosure, methods for efficiently managingbuffers in an LTE system have been proposed and described. In theremaining portion of the disclosure, structures and methods forefficiently managing buffers and accelerating retransmission in anext-generation mobile communication system are proposed.

FIGS. 15A and 15B are diagrams illustrating a data processing structurein a next-generation mobile communication system according to anembodiment of the disclosure.

Referring to FIGS. 15A and 15B, a next-generation mobile communicationsystem performs PDCP-layer and RLC-layer data processing for logicalchannels. That is, logical channel 1 1505 and logical channel 2 1510have different PDCP layers and RLC layers, and perform independent dataprocessing. Further, the next-generation mobile communication systemtransfers RLC PDUs generated from RLC layers 1515 of the respectivelogical channels to a MAC layer 1520 to configure one MAC PDU, andtransmits the MAC PDU to a receiving end. In the next-generation mobilecommunication system, the PDCP layer, the RLC layer, and the MAC layermay include the functions as described above with reference to FIG. 4,and may perform operations corresponding to the functions.

In the next-generation mobile communication system, it is featured thatthe RLC layer does not concatenate the PDCP PDUs. Further, in thenext-generation mobile communication system, a MAC PDU structure, suchas reference numeral 1525, is featured to have a structure having MACsub-headers for each MAC SDU, in other words, a structure in which theMAC sub-headers are repeated in the unit of MAC SDU. Accordingly, in thenext-generation mobile communication system, data preprocessing may beperformed before uplink grant is received at operation 1530.

For example, if the PDCP layer receives IP packets, a terminal of thenext-generation mobile communication system, before receiving uplinkgrant, may perform PDCP processing (ciphering) and integrity protectionwith respect to the received IP packets, and may generate a PDCP PDUthrough generation of a PDCP header. Further, the terminal may configurean RLC PDU by configuring an RLC header through transfer of the PDCPPDUs to the RLC layer, and may pre-configure a MAC sub-header and MACSDUs by transferring the RLC PDU to the MAC layer.

If the terminal receives the uplink grant at operation 1530, it mayconfigure a MAC PDU by bring the MAC sub-header and MAC SDUs to theextent that matches the size of the uplink grant. In contrast, if theuplink grant is insufficient, the terminal may perform a segmentationoperation in order to fill up full and efficiently use transmissionresources. The terminal may update the RLC header (segmented informationor length information) and the MAC header (L field, length changed)corresponding to the segmented data at operation 1540. Accordingly, ascompared with the LTE system, if it is assumed that the uplink grant,such as operation 1530 and operation 1545, is received at the same time,the next-generation mobile communication system can have a great gain inprocessing time, such as reference numeral 1535. If needed, or ifconfigured in the network, the RLC layer and the PDCP layer may use onecommon serial number.

The preprocessing may be performed for each logical channel, and RLCPDUs preprocessed for each logical channel may be preprocessed again asMAC SDUs and a MAC sub-header by the MAC layer. Further, if the MAClayer receives the uplink grant at operation 1530, the terminal maymultiplex the pre-generated MAC SDUs and a MAC sub-header by allocatingthe uplink grant for each logical channel.

After the MAC layer receives the uplink grant from a base station, theterminal may perform LCP, and may divide the uplink grant for eachlogical channel. Further, the terminal may configure one MAC PDU bymultiplexing MAC SDUs and a MAC sub-header generated for each logicalchannel, and transfer the MAC PDU to a physical layer. If the uplinkgrant allocated to each logical channel is insufficient, segmentationmay be requested with respect to the RLC layer. Accordingly, if the RLClayer performs the segmentation operation, segmentation informationincluded in a header may be updated. Further, if the RLC layer transfersthe updated information to the MAC layer again, the MAC layer may updatethe corresponding MAC header. As described above, the next-generationmobile communication system has a feature that data processing of thePDCP layer, RLC layer, and MAC layer starts before the uplink grant isreceived.

Since the next-generation mobile communication system has theabove-described structure, several RLC PDUs may enter into one MAC PDU.In the LTE system, since the RLC layer has a concatenation function,several PDCP PDUs are concatenated to make one RLC PDU to be sent to theMAC layer, and one MAC PDU normally includes RLC PDUs as many as thenumber of logical channels (in the LTE system, the number of logicalchannels is generally about 2 to 4).

However, in the next-generation mobile communication system, the RLClayer does not have an RLC concatenation function, and thus one PDCP PDUis generated as one RLC PDU. Accordingly, one MAC PDU may include RLCPDUs the number of which corresponds to multiplication of the number ofIP packets (PDCP SDUs) by the number of logical channels. Through asimple arithmetic calculation, one MAC PDU may include about 4 RLC PDUsat most in the LTE system, whereas one MAC PDU may include not less than500 RLC PDUs in the next-generation mobile communication system.Accordingly, in the next-generation mobile communication system, if oneMAC PDU is lost, it becomes necessary to retransmit several hundreds ofRLC PDUs. Accordingly, the RLC layer should retransmit several hundredsof RLC PDUs, and this may cause a severe transmission delay.Accordingly, in the disclosure, structures and methods capable ofaccelerating the retransmission in the next-generation mobilecommunication system are proposed.

In the next-generation mobile communication system, the RLC layer mayoperate in an RLC acknowledged mode (RLC AM), an RLC unacknowledged mode(RLC UM), and an RLC transparent mode (RLC TM). IN the RMC AM mode, theRLC layer supports an ARQ function, the transmitting end can receive anRLC status report from the receiving end, and the transmitting end canretransmit negatively acknowledged RLC PDUs using the status report.Accordingly, errorless reliable data transmission is guaranteed.Accordingly, the RLC AM mode is suitable to services requiring highreliability.

In contrast, in the RLC UM mode, the ARQ function is not supported.Accordingly, in the RLC UM mode, the transmitting end does not receivethe RLC status report from the receiving end, and does not perform theretransmission function. In the RLC UM mode, if the uplink grant isreceived, the RLC layer of the transmitting end serves to concatenatethe PDCP PDUs (RLC SDUs) received from an upper layer and tocontinuously transfer the concatenated PDCP PDUs to a lower layer.Accordingly, continuous data transmission without transmission delaybecomes possible, and thus the RLC UM mode is useful to services thatare sensitive to the transmission delay. In the RLC TM mode, the RLClayer directly transmits the PDCP PDUs received from the upper layer tothe lower layer without performing any process. In the TM mode of theRLC layer, data from the upper layer is transparently transferred fromthe RLC layer to the lower layer. Accordingly, the RLC TM mode can beusefully used when transmitting system information or a paging messagetransmitted through a common channel such as a CCCH.

In the disclosure, the PDCP layer and the RLC layer handle an efficientbuffer management method and a retransmission acceleration method, andthus the RLC AM mode and the RLC UM mode excluding the mode in which theRLC layer does not perform any processing, such as the RLC TM mode, willnow be described in detail.

Buffer structure in RLC AM/TM of next-generation mobile communicationsystem and retransmission acceleration.

FIG. 16 is a diagram illustrating a mapping table and a retransmissionacceleration method suitable when a next-generation mobile communicationsystem terminal operates in an RLC AM mode according to an embodiment ofthe disclosure.

Referring to FIG. 16, a terminal has a fifth buffer and a sixth bufferfor respective logical channels. For convenience, FIG. 16 explains onelogical channel. The fifth and sixth buffers of the logical channels maybe physically divided buffers, or physically the same, but logicallydivided buffers. Preferably, the fifth buffer may be a PDCP buffer, andthe sixth buffer may be a MAC buffer. In the disclosure, when actuallyimplemented, the buffers include physically or logically dividablebuffer structures.

The terminal may store IP packets (PDCP SDUs) 1610 entering into a PDCPlayer, and may generate a header of the PDCP SDUs. Further, the terminalmay make a PDCP PDU 1615 by configuring the generated header togetherwith the PDCP SDUs to store them in the fifth buffer 1605. Further, theterminal may perform data preprocessing before receiving uplink grantfrom the base station. Specifically, the terminal may configure an RLCPDU 1620 by generating an RLC header with respect to the PDCP PDUs inthe fifth buffer, configure MAC sub-headers with respect to the RLC PDUs(MAC SDUs), and store the MAC SDUs and the MAC sub-headers together inthe sixth buffer 1630 at operation 1625. However, if all the PDCP PDUsare preprocessed to the MAC SDUs and MAC sub-headers, the sixth buffermay require a large capacity. Accordingly, in the disclosure, the datapreprocessing of the PDCP PDUs may be performed only up to the maximumtransport block (TB) size supported by the terminal and the network.

For example, the terminal may preprocess data only up to a moment whenthe sum of sizes of the data-preprocessed MAC SDUs and MAC sub-headersexceeds the maximum TB size (this is because the size of the PDECP PDUis variable, and thus the sum of the sizes of the MAC SDUs and MACsub-headers may not coincide with the maximum TB size). Further, theterminal may preprocess data only to the extent approximating themaximum TB size. For example, if the size of the data-preprocessed MACSDUs and MAC sub-headers (stored for being transmitted to the sixthbuffer) approximately becomes the maximum TB size, the terminal may notperform the data preprocessing any further.

If the RLC PDU is generated during the data preprocessing, the terminalmay allocate an RLC serial number, preprocess a memory address 1655 ofthe fifth buffer for the PDCP PDUs constituting the RLC PDU and the MACSDUs and MAC sub-headers corresponding to the RLC PDU, and store amemory address 1660 of the sixth buffer in the mapping table 1650. Ifnecessary, the terminal may store the corresponding PDCP serial number.However, in the next-generation mobile communication system, if the PDCPserial number and the RLC serial number are the same, the PDCP serialnumber or the RLC serial number may be omitted. Further, in thenext-generation mobile communication system, even if the PDCP layer andthe RLC layer use one common serial number, the PDCP serial number orthe RLC PDCP serial number may be omitted.

If an uplink grant is received, the terminal distributes the uplinkgrant to the respective logical channels by reflecting priorities or QoSfor the respective logical channels. If the uplink grant 1635 isreceived, the terminal configures a part of a MAC PDU 1645 by bringingdata to the extent corresponding to the uplink grant in the unit of MACsub-header and MAC SDU from the sixth buffer. Further, with respect toother logical channels, the terminal may complete one MAC PDU 1645 bymultiplexing the MAC sub-header 1640 and MAC SDUs received through theabove-described procedure, and may transmit the MAC PDU to a physicallayer.

If the sizes of the MAC sub-headers and the MAC SDUs do not accuratelycoincide with each other when data is added to the uplink grant in theunit of the MAC sub-header and MAC SDU for each logical channel, the RLClayer may perform a segmentation operation with respect to the last RLCSDU that becomes inconsistent with the sizes. If the segmentation isperformed with respect to the RLC SDUs, the RLC layer may newly inputand update the segmentation information to the header of the RLC PDUs.Further, with respect to the completed RLC PDU, the MAC layer may newlyupdate a new MAC sub-headers and may configure MAC sub-headers and MACSDUs to match the uplink grant.

If the RLC layer performs the segmentation operation as described above,information on a header field for the segmentation operation may berecorded in a mapping table at operation 1665. However, if unnecessary,such recording may be omitted. The RLC SDU segmentation operation asdescribed above is featured so that the segmented RLC PDU has asegmentation information field indicating whether the segmented segmentis the first, intermediate, or last segment in a state where thesegmented RLC PDUs maintain the same RLC serial number, and a fieldincluding an offset indicating what location of the original RLC SDU thesegment corresponds to.

If an ACK/NACK is identified through an RLC status report received fromthe RLC layer of the receiving end, the terminal may record thisinformation in the mapping table at operation 1670. If it is necessaryto retransmit the negatively acknowledged RLC PDUs, the RLC layer of thetransmitting end may immediately perform the retransmission by accessingmemory addresses of the previously made and transmitted MAC SDUs and MACsub-headers corresponding to the RLC PDUs using memory addressinformation of the sixth buffer in mapping table 1650. If the uplinkgrant is large enough to include all the RLC PDUs for which theretransmission should be performed, the retransmission may be performedusing the MAC SDUs and MAC sub-headers stored in the sixth buffer. Incontrast, if the uplink is unable to include all the RLC PDUs for whichthe retransmission should be performed, the RLC layer performs thesegmentation operation with respect to the last MAC SDU (RLC PDU), andthe RLC header and the MAC layer perform a procedure of updating the MACheader to perform the retransmission. Further, if it is required toretransmit several successive RLC PDUs at a time, the terminal canperform rapid retransmission with small memory accesses by using thememory address of the sixth buffer in the mapping table 1650. Forexample, the MAC PDUs can be configured by bringing the several RLC PDUsfrom the sixth buffers at a time with reference to a start link of thefirst RLC PDU and an end link of the last RLC PDU among the severalsuccessive RLC PDUs. For example, if it is required to retransmit RLCserial numbers 1 to 6, the terminal may identify the memory address 1655of the sixth buffer from the mapping table 1650, and perform theretransmission using memory addresses 0 to m of the sixth buffer withreference to the start link p of the sixth buffer for the RLC serialnumber 1 and the end link m for the RLC serial number 6.

In a fourth embodiment of an efficient buffer management method and aretransmission acceleration method suitable when a terminal of thenext-generation mobile communication system operates in an RLC AM modeproposed in the disclosure, the terminal may store in the sixth bufferthe MAC sub-headers and MAC SDUs for which the data preprocessing of thePDCP PDU stored in the fifth buffer has been performed, and mayconfigure the mapping table based on the RLC serial number for managingthem. Further, in the fourth embodiment, if it is necessary to performthe retransmission, it is featured to immediately perform theretransmission using the mapping table information in the sixth bufferhaving been pre-generated and stored without the necessity ofregenerating the RLC headers and MAC sub-headers.

Accordingly, even if it is necessary to perform the retransmission ofseveral hundreds of RLC PDUs in the next-generation mobile communicationsystem, the terminal can rapidly retransmit the RLC PDUsdata-preprocessed and stored in the sixth buffer using the mapping tableinformation without the necessity of newly configuring several hundredsof RLC headers and MAC sub-headers. If a segmentation operation isnecessary for each logical channel, it is enough to update only one RLCheader and one MAC header corresponding to the last MAC SDU, and thusthe transmission delay is greatly reduced.

The operations of the fifth buffer and the sixth buffer are as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the fifth buffer 1605 through allocation ofmemory addresses to the IP packets. Further, the PDCP layer may driveand manage a PDCP discard timer for each IP packet. A timer value may beconfigured by a network. For example, when the terminal configures anRRC connection, the timer value may be configured by the network throughan RRC message. If the timer expires, the terminal discards the PDCP PDUor the PDCP SDU corresponding to the timer from the fifth buffer. If thePDCP PDU corresponding to the timer is transmitted to the RLC layer, thePDCP layer transmits a discard indicator corresponding to the PDCP PDUto the RLC layer. The discard indicator may indicate a PDCP PDU serialnumber transmitted to the RLC layer or mapping information on the PDCPPDU.

Further, if ACK/NACK information on the PDCP PDUs is received from thePDCP layer of the receiving end through a PDCP status report, the PDCPlayer may discard the acknowledged PDCP PDUs from the fifth buffer.Further, if an unexpired timer corresponding to the discarded PDCP PDUsexists, it may stop and discard the timer. Further, the PDCP layer mayreceive from the RLC layer information on the PDCP PDUs corresponding tothe RLC PDUs having received the RLC ACK. Since the PDCP PDUs mean thatthey have been successfully transferred to the receiving end, it is notnecessary to store them in the fifth buffer any more. Accordingly, thecorresponding information and mapping table information may bediscarded, and if there exists an unexpired timer, the timer may also bestopped and discarded. In case of managing the fifth buffer based on theRLC ACK, it is significant to differently manage the fifth buffer inaccordance with the PDCP layer operation of the terminal during ahandover.

As a first case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should retransmit thePDCP PDUs to a target base station of the handover again after thelowest PDCP serial number successfully transferred in order up to nowduring the handover. In this case, if information on the PDCP PDUscorresponding to the RLC PDUs having received the RLC ACK is received,the PDCP layer should store the lowest PDCP serial number havingreceived all the ACKs in the order of PDCP serial numbers. Further, withrespect to the PDCP serial numbers that are higher than the lowest PDCPserial number, the PDCP layer should not discard them even if the RLClayer has received the RLC ACK. That is, the PDCP PDUs of which thesuccessful transfer has been identified based on the RLC ACK can bediscarded only in the order of their PDCP serial numbers. For example,even if it is identified that PDCP serial numbers 1, 2, 3, 4, 5, 9, and10 have been successfully transferred from the RLC ACK of the RLC layer,only the PDCP serial numbers 1, 2, 3, 4, and 5 can be discarded from thefifth buffer together with information related to the corresponding PDCPPDUs and mapping information.

As a second case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should selectivelyretransmit the PDCP PDUs having not been successfully transferred up tonow to the target base station of the handover. In this case, ifinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK is received, the PDCP layer may discard theinformation corresponding to the PDCP PDUs and the mapping informationfrom the fifth buffer, and may separately store the information on thePDCP serial numbers having received the ACK in order to use theinformation during the handover.

If the discard indicator is received from the PDCP layer, the RLC layermay discard the corresponding information in a state where the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU, data preprocessing has not been performed with the MAC SDUs andthe MAC sub-header, or the PDCP PDU has not been mapped thereon. Forexample, the RLC layer discards information related to the PDCP PDU (RLCSDU) transferred to and stored in the RLC layer and mapping information.If the PDCP PDU indicated by the discard indicator has already becomethe part of the RLC PDU, the RLC layer does not discard the informationrelated to the PDCP PDU in case where the data preprocessing has beenperformed with the MAC SDUs and the MAC sub-header. This is because ifthe PDCP PDU that has already become the part of the RLC PDU isdiscarded, a gap occurs in the RLC serial number to cause a transmissiondelay.

The receiving end is unable to discriminate whether the correspondingRLC serial number is lost in the transmission process or is discarded bythe discard indicator in the transmitting end. If the RLC status reportis received from the RLC layer of the receiving end, the RLC layer mayidentify the ACK/NACK result for each RLC serial number. Further, incase of the acknowledged RLC PDU, the RLC layer may discard the mappingtable 1650 related to this. The RLC layer transfers information on thePDCP PDU corresponding to the acknowledged RLC PDU, and discards thecorresponding MAC sub-header and MAC SDUs from the sixth buffer storingthe acknowledged preprocessed RLC PDU.

In case of the negatively acknowledged RLC PDU, the RLC layer preparesretransmission thereof. If the uplink grant is sufficient in case wherethe retransmission is performed, the RLC layer may perform theretransmission with reference to the MAC sub-header and the MAC SDUsfrom the sixth buffer using mapping table information. Further, if theuplink grant is insufficient, the RLC layer may perform re-segmentationwith respect to the MAC sub-header and the RLC SDU of the last one ofthe MAC SDUs in the sixth buffer, and may update and retransmit the RLCheader and the MAC header.

The RLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table information(1670), and determine the ACK/NACK result for the corresponding PDCPserial number. If the ACK for the PDCP serial number is identified, theRLC layer may transfer the ACK information for the PDCP serial number tothe PDCP layer. The PDCP layer may identify the ACK information, recordthe ACK/NACK information for each PDCP serial number, and use the ACKinformation to discard the PDCP PDU of the fifth buffer. The ACKinformation for the PDCP serial numbers may be used during a handover.When a terminal handover occurs, the PDCP layer may performretransmission to a target base station of the handover, starting fromthe PDCP serial number after the lowest PDCP serial number havingreceived all the ACKs in the order of serial numbers. If the networksupports a selective retransmission during the handover, the PDCP layermay retransmit only negatively acknowledged PDCP PDUs to the target basestation of the handover.

In the fourth embodiment of an efficient buffer management method and aretransmission acceleration method suitable when a terminal of thenext-generation mobile communication system operates in an RLC AM modeproposed in the disclosure, it is featured that the fifth buffer is notindependently managed by the PDCP layer, but the fifth buffer and thesixth buffer are managed by reflecting the RLC ACK result of the RLClayer. Further, in a fourth embodiment of an efficient buffer managementmethod and a retransmission acceleration method suitable when theterminal of the next-generation mobile communication system operates inan RLC UM mode, it is featured that the fifth buffer is notindependently managed by the PDCP layer, but the fifth buffer and thesixth buffer are managed by reflecting whether to transmit the RLC PDUin the RLC layer.

If an RLC status report is received from the receiving end RLC deviceand an ACK for RLC PDUs is received in an RLC AM mode, it is notnecessary for the RLC device to have information corresponding to theacknowledged RLC PDUs and mapping table information any further, and itis reasonable for the RLC device to discard them from the fifth buffer.Further, if the PDCP PDUs corresponding to the RLC PDUs having receivedthe ACK exist in the fifth buffer, and data-preprocessed MAC SDUs andMAC sub-headers exist in the sixth buffer, such information is not to beused for retransmission, and thus it is not necessary for the RLC layerto have them any further even if a PDCP discard timer has not yetexpired. Accordingly, in the fourth embodiment of the efficient buffermanagement method and the retransmission acceleration method suitablewhen the terminal of the next-generation mobile communication systemaccording to the disclosure operates in the RLC AM mode, it is featuredthat the RLC layer discards information on the RLC PDUs having receivedthe RLC ACK from the mapping table, notifies the PDCP layer of the PDCPPDUs corresponding to the RLC PDUs, discards the corresponding PDCP PDUsfrom the fifth buffer, discards the data-preprocessed MAC sub-header andthe MAC SDUs from the sixth buffer, releases and discards thecorresponding information and timer.

A fourth embodiment of an efficient buffer management method suitablewhen a terminal of a next-generation mobile communication systemaccording to the disclosure having the structure as shown in FIG. 16operates in an RLC UM mode is as follow.

When operating in the RLC UM mode, the terminal according to thedisclosure has the structure as shown in FIG. 16, and operates in asimilar manner to that as described above with reference to FIG. 16.However, different from the RLC AM mode, an ARQ function is notsupported in the RLC UM mode, and thus retransmission is not performed.Further, an RLC status report is not performed. Accordingly, it is notnecessary for the transmitting end to record already transmitted RLCPDUs or related information, and mapping table information for theretransmission. This is the greatest difference between the RLC UM modeand the RLC AM mode. That is, in case of completing the transmission, itis not necessary to store an RLC PDU through data preprocessing of aPDCP PDU, MAC SDU, and MAC sub-headers for the retransmission.

In the disclosure, a fourth embodiment of a method in which a terminalof a next-generation mobile communication system in an RLC UM modeefficiently manages buffers is as follows.

If IP packets are received from an upper layer, the PDCP layer may storethe respective IP packets in the fifth buffer 1605 through allocation ofmemory addresses to the IP packets. Further, the PDCP layer may driveand manage a PDCP discard timer for each IP packet. A timer value may beconfigured by a network. For example, when the terminal configures anRRC connection, the timer value may be configured by the network throughan RRC message. If the timer expires, the terminal discards the PDCP PDUor the PDCP SDU corresponding to the timer from the fifth buffer. If thePDCP PDU corresponding to the timer is transmitted to the RLC layer, thePDCP layer may transmit a discard indicator corresponding to the PDCPPDU to the RLC layer. The discard indicator may indicate a PDCP PDUserial number transmitted to the RLC layer or mapping information on thePDCP PDU. Further, if ACK/NACK information on the PDCP PDUs is receivedfrom the PDCP layer of the receiving end through a PDCP status report,the PDCP layer may discard the acknowledged PDCP PDUs from the fifthbuffer. Further, if an unexpired timer corresponding to the discardedPDCP PDUs exists, the PDCP layer may stop and discard the timer.

If the discard indicator is received from the PDCP layer, the RLC layermay discard the corresponding information in a state where the PDCP PDUcorresponding to the discard indicator has not yet become a part of theRLC PDU in the RLC layer or has not been mapped thereon. For example,the RLC layer discards information related to the PDCP PDU (RLC SDU)transferred to and stored in the RLC layer and mapping information. Ifthe PDCP PDU indicated by the discard indicator has already become apart of the RLC PDU, the RLC layer does not discard the informationrelated to the PDCP PDU indicated by the discard indicator. This isbecause if the PDCP PDU that has already become the part of the RLC PDUis discarded, a gap occurs in the RLC serial number to cause atransmission delay. The receiving end is unable to discriminate whetherthe corresponding RLC serial number is lost in the transmission processor is discarded by the discard indicator in the transmitting end.

The RLC layer may configure RLC PDUs through data preprocessing of thePDCP PDUs before receiving uplink grant, and complete and transfer theRLC PDUs to a MAC layer to store MAC sub-header and MAC SDUs in thesixth buffer. After completing and transferring the RLC PDUs to the MAClayer, the RLC layer discards information related to the RLC PDUs,mapping information, MAC sub-header, and MAC SDUs. In other words, inthe RLC UM mode, the RLC layer transmits the RLC PDUs, and then discardsthem together with the related information, if any, without storingthem. This is because the ARQ function is not supported in the RLC UMmode, and thus it is not necessary to record the information for theretransmission.

In the RLC UM mode, the ARQ function is not supported, and thus it isnot necessary to store the corresponding information after the RLC PDUsare transmitted for the retransmission. Accordingly, after transmittingthe RLC PDUs, the RLC layer does not store in the sixth buffer thecorresponding RLC PDUs, MAC sub-header, MAC SDUs, and related mappinginformation, but discards the related information, if any. Further, oncethe RLC PDUs are transmitted, it is not necessary for the RLC layer tohave the PDCP PDUs corresponding to the RLC PDUs any further even if thePDCP discard timer has not yet expired.

Accordingly, in the fourth embodiment of the efficient buffer managementmethod suitable when the LTE system terminal according to the disclosureoperates in the RLC UM mode, the RLC layer may not store thecorresponding RLC PDUs, MAC sub-headers, and MAC SDUs in the sixthbuffer and the mapping table after transmitting the RLC PDUs, but maydiscard the related information and mapping information, if any.Further, information on the PDCP PDUs corresponding to the RLC PDUs issent to the PDCP layer, and the PDCP layer discards the information onthe PDCP PDUs from the fifth buffer even if the PDCP timer has notexpired.

Terminal data preprocessing and retransmission.

The embodiments of the disclosure as described above may apply a datapreprocessing process to the next-generation mobile communicationsystem. The data preprocessing process may be performed as large as theamount of data capable of being maximally transmitted in one TTI or oncetransmission. That is, the data preprocessing can be performed as muchas the maximum allowable UL grant or the largest UL grant. Further, thetime when the data preprocessing is performed may include one or more ofthe following cases.

1. The data preprocessing can be performed if the amount of thecurrently preprocessed data becomes smaller than the maximum allowableUL grant as described above.

2. The data preprocessing can be periodically performed based on aspecific time.

3. The data preprocessing can be performed at a time when the MAC layerconfigures MAC PDUs using uplink grant and transfers data to thephysical layer.

4. The data preprocessing can be performed after new data istransmitted.

5. Data reception can be performed if an indicator to perform the datapreprocessing is received from a lower layer.

At one of the above-described time points, the terminal can perform thedata preprocessing. Further, if necessary, the terminal can perform thedata preprocessing in accordance with several time points as describedabove.

In case of an RLC control PDU dynamically generated in the RLC layer,for example, in case of generating an RLC status report (RLC statusPDU), the terminal may first generate the RLC status report at a timewhen the data preprocessing is performed, and may perform the datapreprocessing with respect to the RLC status report preferentially toother general RLC PDUs. Further, the terminal may also preferentiallyperform the data preprocessing with respect to RLC PDUs to beretransmitted.

That is, at the time when the above-described data preprocessing isperformed, the terminal may perform the data preprocessing in the orderof the RLC status report, the retransmitted data RLC PDU, and the dataRLC PDU.

Terminal segmentation performing method.

In the above-described process, it is necessary to further specify theprocedure for the terminal to perform the segmentation. That is, if theuplink grant is received in a state where the terminal stores thedata-preprocessed MAC SDUs and MAC sub-headers for each logical channel,the terminal may perform a (LCP procedure in consideration of logicalchannel priority, priority bit rate (PBR), numerology, and TTI values,and may allocate the uplink grant for each logical channel. If aninteger number of sums of the data-preprocessed MAC SDU and MACsub-header units exceeds the uplink grant when the uplink grant isallocated for each logical channel, it may be necessary to perform thesegmentation.

A first embodiment of the segmentation is as follows.

In the first embodiment, the RLC layer may store the RLC PDUstransferred to the MAC layer for the segmentation. The MAC layer maycompare the uplink grant allocated for each logical channel with theinteger number of sums of the data-preprocessed MAC SDU and MACsub-header units, and if the uplink grant is insufficient, the MAC layermay transfer to the RLC layer information on the RLC serial numbercorresponding to the last MAC SDU (RLC PDU). The RLC layer may performthe segmentation with respect to the RLC PDU corresponding to thetransferred RLC serial number, and may transfer the segmented RLC PDUsegments to the MAC layer.

The MAC layer may configure MAC sub-headers with respect to thetransferred RLC PDU segments, and may perform data multiplexing orconcatenation to match the uplink grant. The RLC layer may perform thedata preprocessing and the segmentation in accordance with the uplinkgrant, and in this case, the RLC layer perform the segmentation to matchthe size of the uplink grant allocated for each logical channel inconsideration of the size of the RLC header considering added fields,such as a segmentation offset (SO) field, that may be added to the RLCheader, and the size of the MAC sub-header to be updated later.

A second embodiment of the segmentation is as follows.

In the second embodiment, the RLC layer may not store the RLC PDUstransferred to the MAC layer for the segmentation. The MAC layer maycompare the uplink grant allocated for each logical channel with theinteger number of sums of the data-preprocessed MAC SDU and MACsub-header units, and if the uplink grant is insufficient, the MAC layermay transfer to the RLC layer information on the RLC serial numbercorresponding to the last MAC SDU (RLC PDU). The RLC layer maydynamically regenerate the RLC PDU corresponding to the transferred RLCserial number based on the PDCP PDUs using the mapping tableinformation, perform the segmentation with respect to the generated RLCPDU, and transfer the segmented RLC PDU segments to the MAC layer. TheMAC layer may configure MAC sub-headers with respect to the transferredRLC PDU segments, and may perform data multiplexing or concatenation tomatch the uplink grant. The RLC layer may perform the data preprocessingand the segmentation in accordance with the uplink grant, and in thiscase, the RLC layer perform the segmentation to match the size of theuplink grant allocated for each logical channel in consideration of thesize of the RLC header considering added fields, such as a SO field,that may be added to the RLC header, and the size of the MAC sub-headerto be updated later.

A third embodiment of the segmentation is as follows.

In the third embodiment, the RLC layer may not store the RLC PDUstransferred to the MAC layer for the segmentation. The MAC layer maycompare the uplink grant allocated for each logical channel with theinteger number of sums of the data-preprocessed MAC SDU and MACsub-header units, and if the uplink grant is insufficient, the MAC layermay transfer the last MAC SDU (RLC PDU) to the RLC layer. Then, the RLClayer may perform the segmentation with respect to the transferred RLCPDU, and may transfer the segmented RLC PDU segments to the MAC layer.The MAC layer may configure MAC sub-headers with respect to thetransferred RLC PDU segments, and may perform data multiplexing orconcatenation to match the uplink grant. The RLC layer may perform thedata preprocessing and the segmentation in accordance with the uplinkgrant, and in this case, the RLC layer perform the segmentation to matchthe size of the uplink grant allocated for each logical channel inconsideration of the size of the RLC header considering added fields,such as a SO field, that may be added to the RLC header, and the size ofthe MAC sub-header to be updated later.

A fourth embodiment of the segmentation is as follows.

In the fourth embodiment, the RLC layer may not store the RLC PDUstransferred to the MAC layer for the segmentation. The MAC layer maycompare the uplink grant allocated for each logical channel with theinteger number of sums of the data-preprocessed MAC SDU and MACsub-header units, and if the uplink grant is insufficient, the MAC layermay transfer mapping information (e.g., memory address) for the last MACSDU (RLC PDU) to the RLC layer using a mapping table. Then, the RLClayer may bring the stored RLC PDU using the mapping information,perform the segmentation with respect to the RLC PDU, and may transferthe segmented RLC PDU segments to the MAC layer. The MAC layer mayconfigure MAC sub-headers with respect to the transferred RLC PDUsegments, and may perform data multiplexing or concatenation to matchthe uplink grant.

The RLC layer may perform the data preprocessing and the segmentation inaccordance with the uplink grant, and in this case, the RLC layerperform the segmentation to match the size of the uplink grant allocatedfor each logical channel in consideration of the size of the RLC headerconsidering added fields, such as a SO field, that may be added to theRLC header, and the size of the MAC sub-header to be updated later.

A fifth embodiment of the segmentation is as follows.

In the fifth embodiment, the RLC layer may not store the RLC PDUstransferred to the MAC layer for the segmentation. The MAC layer maycompare the uplink grant allocated for each logical channel with theinteger number of sums of the data-preprocessed MAC SDU and MACsub-header units, and if the uplink grant is insufficient, the MAC layermay transfer mapping information (e.g., memory address) for the last MACSDU (RLC PDU) to the RLC layer using a mapping table. Then, the RLClayer may regenerate the RLC PDU based on the PDCP PDUs using thetransferred mapping information, perform the segmentation with respectto the RLC PDU, and may transfer the segmented RLC PDU segments to theMAC layer. The MAC layer may configure MAC sub-headers with respect tothe transferred RLC PDU segments, and may perform data multiplexing orconcatenation to match the uplink grant.

The RLC layer may perform the data preprocessing and the segmentation inaccordance with the uplink grant, and in this case, the RLC layerperform the segmentation to match the size of the uplink grant allocatedfor each logical channel in consideration of the size of the RLC headerconsidering added fields, such as a SO field, that may be added to theRLC header, and the size of the MAC sub-header to be updated later.

Terminal data preprocessing performing method for multi-connectivity.

In order to perform data preprocessing in a multi-connectivity ordual-connectivity environment, the terminal should be able topredetermine whether a master cell group or a secondary cell group is totransmit data of a PDCP layer. That is, since it is required to allocatean RLC serial number in the data preprocessing process, it should bepredetermined what cell group is to perform the transmission in order toperform the data preprocessing. In the dual-connectivity environment,methods for pre-allocating the PDCP layer data to the master cell groupand the secondary cell group are as follows.

FIG. 21 is a diagram illustrating a method for preprocessing data of amulti-connection terminal according to an embodiment of the disclosure.

1. First allocation method at operation 2101: If the amount of data ofthe PDCP layer is smaller than a predetermined threshold value, theterminal does not pre-allocate the data of the PDCP layer to a mastercell group and a secondary cell group. The data within the thresholdvalue is preprocessed only in the master cell group (or secondary cellgroup). Further, if the amount of data of the PDCP layer becomes largerthan the threshold value, the terminal does not perform the datapreprocessing with respect to the data of which the amount is largerthan the threshold value, but performs buffer status report to themaster cell group and the secondary cell group with respect to thecurrent amount of data of the PDCP layer. Further, if the uplink grantis received with respect to each cell group, the terminal may allocatethe PDCP layer data to the master cell group and the secondary cellgroup in accordance with the uplink grant, and may perform datapreprocessing to transmit the data. The threshold value may be allocatedas a value capable of indicating a low data rate or small data, and maybe configured when the network (or base station) performs RRC connectionconfiguration.

2. The (1-1)-th allocation method at operation 2102: If the amount ofdata of the PDCP layer is smaller than a predetermined threshold value,the terminal does not pre-allocate the data of the PDCP layer to amaster cell group and a secondary cell group. The data within thethreshold value is preprocessed only in the master cell group (orsecondary cell group). Further, if the amount of data of the PDCP layerbecomes larger than the threshold value, the terminal may preprocessdata as much as the threshold value only with respect to the master cellgroup, and may perform buffer status report to the master cell group andthe secondary cell group with respect to the data exceeding thethreshold value. Further, if the uplink grant is received with respectto each cell group, the terminal may allocate the PDCP layer data to themaster cell group and the secondary cell group in accordance with theuplink grant, and may perform data preprocessing to transmit the data.The threshold value may be allocated as a value capable of indicating alow data rate or small data, and may be configured when the network (orbase station) performs RRC connection configuration.

3. The (1-2)-th allocation method at operation 2103: If the amount ofdata of the PDCP layer is smaller than a predetermined threshold value,the terminal does not pre-allocate the data of the PDCP layer to amaster cell group and a secondary cell group. The data within thethreshold value is preprocessed only in the master cell group (orsecondary cell group). Further, if the amount of data of the PDCP layerbecomes larger than the threshold value, the terminal may preprocessdata as much as the threshold value with respect to the master cellgroup, and may preprocess data exceeding the threshold value withrespect to the secondary cell group as much as the size of the uplinkgrant that can be maximally allocated of the secondary cell group.Further, with respect to the remaining data, the terminal may performbuffer status report, and if the uplink grant is received with respectto each cell group, the terminal may allocate the PDCP layer data to themaster cell group and the secondary cell group in accordance with theuplink grant, and may perform data preprocessing to transmit the data.The threshold value may be allocated as a value capable of indicating alow data rate or small data, and may be configured when the network (orbase station) performs RRC connection configuration.

4. Second allocation method at operation 2104: If the amount of data ofthe PDCP layer is smaller than a predetermined threshold value, theterminal does not pre-allocate the data of the PDCP layer to a mastercell group and a secondary cell group. The data within the thresholdvalue is preprocessed only in the master cell group (or secondary cellgroup). Further, if the amount of data of the PDCP layer becomes largerthan the threshold value, the terminal may pre-allocate the currentoverall data of the PDCP layer to the master cell group and thesecondary cell group in accordance with a specific split ratioconfigured by the network or base station (or with respect to the dataas much as the threshold value, data preprocessing is performed for themaster cell group, and with respect to the data exceeding the thresholdvalue, data preprocessing is performed after the data is pre-allocatedto the master cell group and the secondary cell group in accordance withthe specific split ratio). Further, with respect to the pre-allocateddata, the terminal may perform the data preprocessing for the respectivecell groups before the respective cell groups are allocated with theuplink grant. The threshold value may be configured as a value capableof indicating a low data rate or small data, when RRC connectionconfiguration is performed by the network (or base station), and thespecific ratio may be configured when the network (or base station)performs the RRC connection configuration in consideration of thenetwork and base station resource situations.

In the disclosure, the terminal in the dual-connectivity environment canperform the data preprocessing by applying one of four methods asdescribed above.

A procedure in which the PDCP layer of the terminal determines theamount of data based on the threshold value and pre-allocates data tothe master cell group and the secondary cell group may start at one orplural time points described as follows.

1. When it is intended to perform the data preprocessing in a statewhere the amount of the currently preprocessed data becomes smaller thanthe amount of uplink grant capable of being maximally allocated

2. Periodically based on a constant time

3. At a time when the MAC layer configures the MAC PDU using the uplinkgrant and transfers data to the physical layer

4. After transmitting new data

5. When an indicator for performing the data preprocessing is receivedfrom the lower layer and it is intended to perform the datapreprocessing

6. Whenever new data is received in the PDCP layer

7. When an indicator to perform data allocation to the master cell groupand the secondary cell group is received from the lower layer

8. When the amount of data becomes larger than a specific thresholdvalue in the PDCP layer

Whenever the amount of data of the PDCP layer is compared with thethreshold value, the amount of data of the PDCP layer may be calculatedby the following methods.

1. First calculation method: This method calculates the size of theoverall data corresponding to the sum of the data amount of the PDCPdata layer that is not transmitted and is not preprocessed, the dataamount that is not transmitted and is preprocessed in the master cellgroup, and the data amount that is not transmitted and is preprocessedin the secondary cell group, and compares the calculated value with thethreshold value.

2. Second calculation method: This method calculates the size of thedata amount of the PDCP data layer that is not transmitted and is notpreprocessed, and compares the calculated value with the thresholdvalue.

3. Third calculation method: This method calculates the size of the dataamount that is not transmitted and is newly received excluding the datacalculated when being compared with the previous threshold value, andcompares the calculated value with the threshold value.

4. Fourth calculation method: This method calculates the size of theoverall data corresponding to the sum of the data amount that is nottransmitted and is preprocessed in the master cell group and the dataamount that is not transmitted and is preprocessed in the secondary cellgroup, and compares the calculated value with the threshold value.

Using one of the four methods as described above, the size of the dataof the PDCP layer to be compared with the threshold value through theterminal in the dual-connectivity environment can be calculated.

The terminal in the dual-connectivity environment may make it a rule toallocate the successive PDCP serial numbers so that the respective cellgroups maximally have them when the data of the PDCP layer ispre-allocated to the master cell group and the secondary cell group. Ifthe PDCP serial numbers are not split to the respective cell groups, butare allocated to the groups of the successive PDCP serial numbers, theprocessing time and burden occurring when the PDCP layer of thereceiving side realigns the order of the PDCP serial numbers can bereduced.

In the method for performing data preprocessing of the terminal in thedual-connectivity environment, the data preprocessing can be performedby applying the method for performing data preprocessing of the terminalin a single-connectivity environment to each cell group. That is, whenperforming the data preprocessing in the respective cell groups, theterminal can perform the data preprocessing as much as the maximumtransport block size, the maximum allowable UL grant, or the size of thedata maximally transmittable in one TTI. That is, although the datapreprocessing is performed as much as the above-described size, it ispossible to obtain the maximum data preprocessing gain for the next datatransmission.

In the method for performing the data preprocessing of the terminal inthe dual-connectivity environment, the threshold value or the specificsplit ratio can be configured from the base station to the terminalthrough an RRC message (RRCConnectionSetup orRRCConnectionReconfiguration), or may be dynamically reconfiguredthrough the RRC message (RRCConnectionReconfiguration). Further, inorder to dynamically allocate the threshold value or the specific splitratio, the threshold value or the specific split ratio may be updatedusing a newly defined PDCP control PDU.

In the method for performing the data preprocessing of the terminal inthe dual-connectivity environment, it is necessary for the base stationto configure the threshold value so that the threshold value becomeslarger than the maximum transport block size of the master cell group,the maximum allowable UL grant, or the data size maximally transmittablein one TTI. This is because it becomes possible to obtain the maximumdata preprocessing gain for the next data transmission by configuringthe threshold value so that it becomes larger than the maximum transportblock size, the maximum allowable UL grant, or the data size maximallytransmittable in one TTI.

In the dual-connectivity environment as described above, the terminalmay configure the data of the PDCP layer to transmit them to differentcell groups through packet duplication, and this configuration may beactivated or inactivated by the RRC message or the newly defined PDCPcontrol PDU.

FIGS. 17A and 17B are diagrams illustrating operation of a terminal inwhich a next-generation mobile communication system terminal managesbuffers in an RLC AM mode according to an embodiment of the disclosure.

Referring to FIG. 17A, if IP packets are received from an upper layer, aterminal PDCP layer may operate at operation 1701, the terminal PDCPlayer may receive an IP packet at operation 1705, and may store therespective IP packets in a fifth buffer through allocation of memoryaddresses to the IP packets at operation 1710. Further, the terminalPDCP layer may drive and manage a PDCP discard timer for each IP packetat operation 1715. If the timer expires, the terminal discards a PDCPPDU or a PDCP SDU corresponding to the timer from the fifth buffer atoperation 1720. If the PDCP PDU corresponding to the timer istransmitted to an RLC layer at operation 1725, the PDCP layer maytransmit a discard indicator corresponding to the PDCP PDU to the RLClayer at operation 1730. The discard indicator may indicate the PDCP PDUserial number transmitted to the RLC layer, or mapping information onthe PDCP PDU. Further, if ACK/NACK information on the PDCP PDUs isreceived from the PDCP layer of the receiving end through a PDCP statusreport, the PDCP layer may discard the acknowledged PDCP PDUs from thefifth buffer. Further, if there exists an unexpired timer correspondingto the discarded PDCP PDUs, the PDCP layer may stop and discard thetimer at operation 1720.

Further, the PDCP layer may receive from the RLC layer information onthe PDCP PDUs concatenated to the RLC PDUs having received the RLC ACK.Since the PDCP PDUs mean that they have been successfully transferred tothe receiving end, it is not necessary to store them in the fifth bufferany more, and the PDCP layer may discard them. The PDCP layer discardsinformation corresponding to the discarded PDCP PDU and mapping tableinformation, and if there exists an unexpired timer, the PDCP layer maystop and discard the timer at operation 1720. In case of managing thefifth buffer based on the RLC ACK, it is significant to differentlymanage the fifth buffer in accordance with the PDCP layer operation ofthe terminal during a handover.

As a first case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should retransmit thePDCP PDUs to a target base station of the handover again after thelowest PDCP serial number successfully transferred in order up to nowduring the handover. In this case, if information on the PDCP PDUsconcatenated to the RLC PDUs having received the RLC ACK is received,the PDCP layer should store the lowest PDCP serial number havingreceived all the ACKs in the order of PDCP serial numbers. Further, withrespect to the PDCP serial numbers that are higher than the lowest PDCPserial number, the PDCP layer should not discard them even if the RLClayer has received the RLC ACK. That is, the PDCP PDUs of which thesuccessful transfer has been identified based on the RLC ACK can bediscarded only in the order of their PDCP serial numbers. For example,even if it is identified that PDCP serial numbers 1, 2, 3, 4, 5, 9, and10 have been successfully transferred from the RLC ACK of the RLC layer,only the PDCP serial numbers 1, 2, 3, 4, and 5 can be discarded from thefifth buffer together with information related to the corresponding PDCPPDUs and mapping information.

As a second case, the terminal may perform the PDCP layer operation witha network configuration in which the PDCP layer should selectivelyretransmit the PDCP PDUs having not been successfully transferred up tonow to the target base station of the handover. In this case, ifinformation on the PDCP PDUs concatenated to the RLC PDUs havingreceived the RLC ACK is received, the PDCP layer may discard theinformation corresponding to the PDCP PDUs and the mapping informationfrom the fifth buffer, and may separately store the information on thePDCP serial numbers having received the ACK in order to use theinformation during the handover.

Referring to FIG. 17B, a terminal RLC layer operates at operation 1735.If the discard indicator is received from the PDCP layer at operation1740, a terminal RLC layer may discard the corresponding information atoperation 1755 when the PDCP PDU corresponding to the discard indicatorhas not yet become a part of the RLC PDU in the RLC layer or has notbeen mapped thereon at operation 1745. That is, the terminal RLC layerdiscards information related to PDCP PDU (RLC SDU) transferred to andstored in the RLC layer and mapping information. If the PDCP PDUindicated by the discard indicator has already become the part of theRLC PDU at operation 1745, the terminal RLC layer does not discard theinformation related to the PDCP PDU at operation 1750.

If the RLC status report is received from the RLC layer of the receivingend at operation 1740, the RLC layer may identify the ACK/NACK resultfor each RLC serial number. Further, in case of the acknowledged RLC PDUat operation 1760, the RLC layer discards from the six buffer themapping information related to the acknowledged RLC PDU, the MACsub-headers and MAC SDUs in which the RLC PDU/PDCP PDU are preprocessedand stored at operation 1765. In contrast, with respect to thenegatively acknowledged RLC PDU, the RLC layer prepares retransmissionat operation 1775.

If the uplink grant for the retransmission is sufficient duringperforming of the retransmission, the RLC layer may rapidly perform theretransmission using the MAC sub-headers and MAC SDUs data-preprocessedby the sixth buffer based on the mapping information for the RLC PDU. Incontrast, if the uplink grant is insufficient, the RLC layer may performre-segmentation to update the RLC headers and MAC sub-headers for thelast MAC sub-header and MAC SDU, and may perform the retransmission. TheRLC layer may identify the result of the ACK/NACK for the RLC serialnumber through the RLC status report, identify mapping table informationat operation 1770, and determine the ACK/NACK result for thecorresponding PDCP serial number. If the ACK for the PDCP serial numberis identified, the RLC layer may transfer the ACK information for thePDCP serial number to the PDCP layer. The PDCP layer may identify theACK information, and may use the ACK information to discard thecorresponding PDCP PDUs from the fifth buffer.

Accordingly, in the fourth embodiment of the efficient buffer managementmethod and the retransmission acceleration method suitable when theterminal of the next-generation mobile communication system operates inthe RLC AM mode according to the disclosure, the RLC layer may discardfrom the fifth buffer information on the RLC PDUs having received theRLC ACK and mapping table information/the data-preprocessed MACsub-headers and MAC SDUs, and the PDCP PDUs corresponding to the RLCPDUs of which the RLC layer has notified the PDCP layer, and release anddiscard the corresponding information and the timer. Accordingly, thebuffer can be efficiently managed even with a small size so as torapidly empty the fifth and sixth buffers, and thus efficiency can bemaximized and the retransmission can be accelerated.

FIGS. 18A and 18B are diagrams illustrating operation of a terminal inwhich a next-generation mobile communication system terminal managesbuffers in an RLC UM mode according to an embodiment of the disclosure.

Referring to FIG. 18A, if IP packets are received from an upper layer, aterminal PDCP layer may operation at operation 1801, the terminal PDCPlayer may receive an IP packet at operation 1805, and may store therespective IP packets in a fifth buffer through allocation of memoryaddresses to the IP packets at operation 1810. Further, the terminalPDCP layer may drive and manage a PDCP discard timer for each IP packetat operation 1815. If the timer expires, the terminal discards a PDCPPDU or a PDCP SDU corresponding to the timer from the fourth buffer atoperation 1820. If the PDCP PDU corresponding to the timer istransmitted to an RLC layer at operation 1825, the PDCP layer maytransmit a discard indicator corresponding to the PDCP PDU to the RLClayer at operation 1830. The discard indicator may indicate a PDCP PDUserial number transmitted to the RLC layer or mapping information on thePDCP PDU. Further, if ACK/NACK information on the PDCP PDUs is receivedfrom the PDCP layer of the receiving end through a PDCP status report,the PDCP layer may discard the acknowledged PDCP PDUs from the fifthbuffer, and if there exists an unexpired timer corresponding to thediscarded PDCP PDUs, the PDCP layer may stop and discard the timer atoperation 1820. Further, if the RLC PDU is transmitted from the RLClayer and the RLC layer transfers to the PDCP layer information on thePDCP PDUs concatenated to the transmitted RLC PDUs, the PDCP layer maydiscard the information on the transmitted PDCP PDUs from the fifthbuffer, and if the corresponding timer has not expired, the PDCP layermay release and discard the timer.

Referring to FIG. 18B, the terminal layer operates at operation 1835. Ifthe discard indicator is received from the PDCP layer at operation 1840,a terminal RLC layer may discard the corresponding information in casewhere the PDCP PDU corresponding to the discard indicator has not yetbecome a part of the RLC PDU in the RLC layer or has not been mappedthereon at operation 1845. That is, the terminal RLC layer discards theinformation related to the PDCP PDU (RLC SDU) transferred to and storedin the RLC layer and mapping information at operation 1855. If the PDCPPDU indicated by the discard indicator has already become a part of theRLC PDU at operation 1845, the terminal RLC layer does not discard theinformation related to the PDCP PDU at operation 1850.

The RLC layer may configure RLC PDUs through data preprocessing of thePDCP PDUs before receiving the uplink grant, and may complete andtransfer the RLC PDU to the MAC layer to store MAC sub-headers and MACSDUs in the sixth buffer. Further, if the RLC PDU transmission iscompleted through reception of the uplink grant, the RLC layer discardsinformation related to the RLC PDUs, mapping information, MACsub-headers, and MAC SDUs (discarded from the sixth buffer) at operation1860. In other words, in the RLC UM mode, the RLC layer transmits theRLC PDUs, and then discards the related information, if any, withoutstoring the RLC PDUs. This is because the ARQ function is not supportedin the RLC UM mode, and thus it is not necessary to record theinformation for the retransmission. Further, the RLC layer may determineand transfer to the PDCP layer information on the PDCP PDUscorresponding to the transmitted RLC PDUs, and may use the informationto manage the fifth buffer at operation 1865.

Accordingly, in the fourth embodiment of the efficient buffer managementmethod suitable when the terminal of the next-generation mobilecommunication system operates in the RLC UM mode, the RLC layertransmits the RLC PDUs, and then may discard related information andcorresponding data-preprocessed MAC sub-headers and MAC SDUs, if any inthe sixth buffer, without storing the corresponding RLC PDUs. Further,in the fourth embodiment, the RLC layer may transmit to the PDCP layerinformation on the PDCP PDUs corresponding to the transmitted RLC PDUs,and the PDCP layer immediately discards the information on the PDCP PDUsfrom the fifth buffer even if the PDCP timer has not expired.

The first to fourth embodiments of the disclosure have proposed thebuffer structure when the terminal transmits data and the retransmissionacceleration method. In the disclosure, when the terminal receives data,the RLC layer may have a separate buffer for storing the RLC PDUs. TheRLC PDUs can indicate only the segmented RLC PDU segments rather thanthe complete RLC PDU (non-segmented RLC PDU or RLC PDU that is not thesegment). That is, if the RLC layer receives the complete RLC PDUs whenthe terminal receives data, it may directly transfer them to an upperlayer without storing them, whereas if the RLC PDU segments arereceived, the RLC layer stores them in a separate buffer for reassembly,and if a specific condition is satisfied, it assembles the RLC PDUsegments into one complete RLC PDU to transfer the complete RLC PDU tothe upper layer. The RLC PDU segments having not been assembled into onecomplete RLC PDU may be all discarded. The specific condition may be acase where a timer for the reassembly has expired or a case where awindow based on the RLC layer serial number moves to trigger thereassembly.

FIG. 19 is a block diagram of a terminal according to an embodiment ofthe disclosure.

Referring to FIG. 19, the terminal includes a radio frequency (RF)processor 1910, a baseband processor 1920, a memory 1930, and acontroller 1940.

The RF processor 1910 performs a function for transmitting and receivinga signal on a radio channel, such as signal band conversion andamplification. That is, the RF processor 1910 performs up-conversion ofa baseband signal provided from the baseband processor 1920 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. For example, the RF processor 1910 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital-to-analog converter (DAC), and ananalog-to-digital converter (ADC). Although only one antenna isillustrated in the drawing, the terminal may be provided with aplurality of antennas. Further, the RF processor 1910 may include aplurality of RF chains. Further, the RF processor 1910 may performbeamforming. For the beamforming, the RF processor 1910 may adjustphases and sizes of signals transmitted or received through theplurality of antennas or antenna elements. Further, the RF processor mayperform MIMO, and may receive several layers during performing of a MIMOoperation. The RF processor 1910 may perform reception beam sweepingthrough proper configuration of the plurality of antennas or antennaelements under the control of the controller, or may control thedirection and the beam width of the reception beam so that the receptionbeam is synchronized with the transmission beam.

The baseband processor 1920 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the system. For example, during data transmission, the basebandprocessor 1920 generates complex symbols by encoding and modulating atransmitted bit string. Further, during data reception, the basebandprocessor 1920 restores a received bit string by demodulating anddecoding the baseband signal provided from the RF processor 1910. Forexample, in the case of following an OFDM method, during datatransmission, the baseband processor 1920 generates complex symbols byencoding and modulating a transmitted bit string, performs mapping ofthe complex symbols on subcarriers, and then configures OFDM symbolsthrough the inverse fast Fourier transform (IFFT) operation and cyclicprefix (CP) insertion. Further, during data reception, the basebandprocessor 1920 divides the baseband signal provided from the RFprocessor 1910 in the unit of OFDM symbols, restores the signals mappedon the subcarriers through the fast Fourier transform (FFT) operation,and then restores the received bit string through demodulation anddecoding.

The baseband processor 1920 and the RF processor 1910 transmit andreceive the signals as described above. Accordingly, the basebandprocessor 1920 and the RF processor 1910 may be called a transmitter, areceiver, a transceiver, or a transceiver. Further, in order to supportdifferent radio connection technologies, at least one of the basebandprocessor 1920 and the RF processor 1910 may include a plurality ofcommunication modules. Further, in order to process signals of differentfrequency bands, at least one of the baseband processor 1920 and the RFprocessor 1910 may include different communication modules. For example,the different radio connection technologies may include an LTE networkand an NR network. Further, the different frequency bands may includesuper high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) band and millimeterwave (mmWave) (e.g., 60 GHz) band.

The memory 1930 stores therein a basic program for an operation of theterminal, application programs, and data of configuration information.The memory 1930 provides stored data in accordance with a request fromthe controller 1940.

The controller 1940 controls the whole operation of the terminal. Forexample, the controller 1940 transmits and receives signals through thebaseband processor 1920 and the RF processor 1910. Further, thecontroller 1940 records or reads data in or from the memory 1930. Forthis, the controller 1940 may include at least one processor thatexecutes instruction to implement a multi-connection processor 19 thatexecutes instruction to implement a multi-connection processor 204242.For example, the controller 1940 may include a communication processor(CP) performing a control for communication and an application processor(AP) controlling an upper layer, such as an application program.

FIG. 20 is a block configuration of a transmission and reception point(TRP) according to an embodiment of the disclosure.

Referring to FIG. 20, the base station includes an RF processor 2010, abaseband processor 2020, a transceiver 2030, a memory 2040, and acontroller 2050.

The RF processor 2010 performs a function for transmitting and receivinga signal on a radio channel, such as signal band conversion andamplification. That is, the RF processor 2010 performs up-conversion ofa baseband signal provided from the baseband processor 2020 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. For example, the RF processor 2010 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a DAC, and an ADC. Although only one antenna isillustrated in the drawing, the first connection node may be providedwith a plurality of antennas. Further, the RF processor 2010 may includea plurality of RF chains. Further, the RF processor 2010 may performbeamforming. For the beamforming, the RF processor 2010 may adjustphases and sizes of signals transmitted or received through theplurality of antennas or antenna elements. Further, the RF processor mayperform down MIMO operation through transmission of one or more layers.

The baseband processor 2020 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the first radio connection technology. For example, during datatransmission, the baseband processor 2020 generates complex symbols byencoding and modulating a transmitted bit string. Further, during datareception, the baseband processor 2020 restores a received bit string bydemodulating and decoding the baseband signal provided from the RFprocessor 2010. For example, in the case of following an OFDM method,during data transmission, the baseband processor 2020 generates complexsymbols by encoding and modulating a transmitted bit string, performsmapping of the complex symbols on subcarriers, and then configures OFDMsymbols through the IFFT operation and CP insertion. Further, duringdata reception, the baseband processor 2020 divides the baseband signalprovided from the RF processor 2010 in the unit of OFDM symbols,restores the signals mapped on the subcarriers through the FFToperation, and then restores the received bit string throughdemodulation and decoding. The baseband processor 2020 and the RFprocessor 2010 transmit and receive the signals as described above.Accordingly, the baseband processor 2020 and the RF processor 2010 maybe called a transmitter, a receiver, a transceiver, a transceiver, or awireless transceiver.

The transceiver 2030 provides an interface for performing communicationwith other nodes in the network.

The memory 2040 stores therein a basic program for an operation of themain base station, application programs, and data of configurationinformation. In particular, the memory 2040 may store information on abearer allocated to the connected terminal and the measurement resultreported from the connected terminal. Further, the memory 2040 may storeinformation that becomes a basis of determination whether to provide orsuspend a multi-connection to the terminal. Further, the memory 2040provides stored data in accordance with a request from the controller2050.

The controller 2050 controls the whole operation of the main basestation. For example, the controller 2050 transmits and receives signalsthrough the baseband processor 2020 and the RF processor 2010 or throughthe transceiver 2030. Further, the controller 2050 records or reads datain or from the memory 2040. For this, the controller 2050 may include atleast one processor that executes instruction to implement amulti-connection processor 2052.

In the drawings explaining the method according to the disclosure, theorder of explanations may not inevitably correspond to the order ofexecutions, and the processes may be executed in a reverse order or inparallel.

Further, in the drawings explaining the method according to thedisclosure, only parts of constituent elements may be included withomission of other parts of the constituent elements without departingfrom the subject matter of the disclosure.

Although preferred embodiments of the disclosure have been described inthe specification and drawings and specific wordings have been used,these are merely used as general meanings to assist those of ordinaryskill in the art to gain a comprehensive understanding of thedisclosure, and do not limit the scope of the disclosure. It will beapparent to those of ordinary skill in the art to which the disclosurepertains that various modifications are possible based on the technicalconcept of the disclosure in addition to the embodiments disclosedherein.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method by an apparatus in a communicationsystem, the method comprising: receiving, in a radio link control (RLC)layer associated with the apparatus, RLC packet data units (PDUs) for anRLC unacknowledged mode (UM) from a lower layer; identifying whether thereceived RLC PDUs are complete RLC PDUs that are non-segmented RLC PDUs;in case that the received RLC PDUs are the complete RLC PDUs,transmitting the complete RLC PDUs to an upper layer without storing thecomplete RLC PDUs in a buffer; and in case that the received RLC PDUsare non-complete RLC PDUs: storing the non-complete RLC PDUs in thebuffer, in case that the non-complete RLC PDUs are reassembled into acomplete RLC PDU, transmitting the complete RLC PDU to the upper layer,and discarding the non-complete RLC PDUs that are not reassembled andstored in the buffer based on a reassembly window in case that thereassembly window is updated based on an RLC PDU sequence number.
 2. Themethod of claim 1, wherein the lower layer is a medium access control(MAC) layer and the upper layer is a packet data convergence protocol(PDCP) layer.
 3. The method of claim 1, wherein discarding thenon-complete PDUs further comprises discarding the non-complete RLC PDUsin case that a reassembly timer expires.
 4. The method of claim 1,wherein the buffer is a first buffer, and wherein transmitting thecomplete RLC PDUs to the upper layer further comprises discarding a MACsubheader and a MAC service data unit (SDU), which correspond to thereceived RLC PDUs, stored in a second buffer.
 5. The method of claim 1,wherein the complete RLC PDUs that are transmitted to the upper layerare reordered by the upper layer.
 6. An apparatus in a communicationsystem, the apparatus comprising: a transceiver; and a controllerconfigured to: receive, in a radio link control (RLC) layer associatedwith the apparatus, RLC packet data units (PDUs) for an RLCunacknowledged mode (UM) from a lower layer, identify whether thereceived RLC PDUs are complete RLC PDUs that are non-segmented RLC PDUs,in case that the received RLC PDUs are the complete RLC PDUs, transmitthe complete RLC PDUs to an upper layer without storing the complete RLCPDUs in a buffer, and in case that the received RLC PDUs arenon-complete RLC PDUs: store the non-complete RLC PDUs in the buffer, incase that the non-complete RLC PDUs are reassembled into a complete RLCPDU, transmitting the complete RLC PDU to the upper layer, and discardthe non-complete RLC PDUs that are not reassembled and stored in thebuffer based on a reassembly window in case that the reassembly windowis updated based on an RLC PDU sequence number.
 7. The apparatus ofclaim 6, wherein the lower layer is a medium access control (MAC) layerand the upper layer is a packet data convergence protocol (PDCP) layer.8. The apparatus of claim 6, wherein the controller is furtherconfigured to discard the non-complete RLC PDUs in case that areassembly timer expires.
 9. The apparatus of claim 6, wherein thebuffer is a first buffer, and wherein the controller is furtherconfigured to discard a MAC subheader and a MAC service data unit (SDU),which correspond to the received RLC PDUs, stored in a second buffer.10. The apparatus of claim 6, wherein the complete RLC PDUs that aretransmitted to the upper layer are reordered by the upper layer.